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PreTinger 

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San Francisco, California 
2007 



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This Volume is for 
REFERENCE USE ONLY 






RADIO BROADCAST 



VOLUME XII 



NOVEMBER, 1927, to APRIL, 1928 




GARDEN CITY NEW YORK 

DOUBLEDAY, DORAN & COMPANY, INC. 

1928 



. - 

: '. 



INDEX 



("Illustrated Articles. Editorials in Italics) 



PAGE 

* A AND B Power Units, Testing 

xTt (Howard E. Rhodes) 443 

*A Power Unit, A New (Ralph Barclay) 350 
*Accessories, Some Reliable Radio 

Power Supply 293 

Action from the Radio Commission 15 

Advertising a Service ? Is Direct 16 

Advertising? What is the Matter with 

Radio 14 

*Air Liner, The Eyes of a Future 

("Anonymous") 271 

*Aircraft Radio? What's the Trouble 

With 11 

*A. C. "Bandbox," the (John F. Rider) 369 
*A. C. Browning-Drake Receiver, An 

(Glenn H. Browning) 343 

*A. C. Loftin- White Receiver, An (John 

F. Rider) 438 

*A. C. Push-Pull Amplifier and B Sup- 
ply, An (J. E. Coombesp 287 

*A. C. Receiver, A Quality Five-Tube 

(James Millen) 135 

*A. C. Super-Heterodyne, A 45-kc 

(Dormand S. Hill) 274 

*A. C. Tubes, Electrification Without 

(Lewis B. Hagerman) 413 

* Amplification Why? Push-Pull (How- 

ard E. Rhodes) 202 

*Applications of the Four-Electrode 

Tube (Theodore H. Nakken) 109 

*Are Programs Going in the Wrong 

Direction? (John Wallace) 219 

* Aristocrat, The Improved (Arthur H. 

Lynch) 46 

*Armchair Engineer, The (Keith Hen- 

ney) 360 

*As the Broadcaster Sees It (Carl 

Dreher) 50, 142, 235, 311, 367, 429 

*D DEVICE Output, Constant (G.F. 

l-> Lampkin) 304 

*B Device Shall I Buy? What (Howard 

E. Rhodes) 120 

""Bandbox," The A. C. (John F. Rider) 369 
*Beauty The Keynote in the New 

Radio Receivers . 118 

Blue Laws of Radio, The 409 

Book Reviews: 

Drake's Radio Cyclopedia, by 

Harold P. Manly (E. H. F.) 236 
Inventions and Patents, Their 
Development and Promotion, 
by Milton Wright (E. H. F.) 125 
Principles of Radio Communi- 
cation, by J. H. Morecroft 

(Carl Dreher) 394 

Story of Radio, The, by Orrin 

E. Dunlap (C. D.) 137 

Booklets Available, Manufacturers' 

62, 153, 244, 320, 392 
Broadcasting Conditions, The Com- 
mission Improves 278 

Broadcasting Conditions, What Readers 

Say About 200 

Broadcasting Situation ? What Is the 

True 346 

*Browning-Drake, Electrifying the 

(James Millen) 33 

*Browning-Drake Receiver, An A. C. 
(Glenn H. Browning) 343 



PAGE 

, Pioneer Picture Broadcast- 
ing Station (Edgar H. Felix) . . 362 
*C. W. Transmitter, A Short-Wave 

Phone and (Kendall Clough) ....... 410 

Can the Serious Problem of Radio Patents 

Be Settled ? ....................... 198 

*"Channel Numbers"? Meters, Kilo- 

cycles, or (Ralph H. Langley) ..... 18 
*Coils, Matching R. F. (F. J. Fox and 

R. F. Shea) ...................... 308 

Commission Announces a New Policy, 

The ............................. 199 

Commission Improves Broadcasting Con- 

ditions, The ...................... 278 

Commission Retreats, The ............ 408 

Commission Suggests Synchronization 

Schemes ......................... 199 

Commissioner Appointed, New ........ 281 

*Concomitants of Good Quality ....... 230 

*Constant B-Device Output (G. F. 

Lampkin) ........................ 304 

*Cooley Picture Receiver, Why I In- 

stalled a (Edgar H. Felix) ......... 215 

*Cooley "Rayfoto" System Works, 

How the (Austin G. Cooley) ........ 23 

DESIGNING an R. F. Amplifier 
(Sylvan Harris) ............... 376 

Direct Advertising a Service ? Is ....... 16 

Directory of Manufactured Receivers, 
"Radio Broadcast's" 

70, 154, 246, 322, 388 
*Do You Own a Battery Operated Set? 
(Howard E. Rhodes) .............. 30 

Does Monopoly Rule the Commission? 346 
*DX Listener Finds a Champion, The 
(John Wallace) ................... 140 

rpDUCATION, University Offerings 
-LL< in Radio (Carl Dreher) ......... 339 

*Electrification Without A. C. Tubes 

(Lewis B. Hagerman) ............. 413 

*Electrifying the Browning-Drake 

(James Millen) ................... 33 

*Electrifying the " Hi-Q " (F. N. Brock) 436 
*Electrifying Your Present Set (Zeh 

Bouck) .......................... 416 

*Engineer, The Armchair (Keith Hen- 

ney ............................. 360 

Engineering To-day, Radio ........... 16 

*"Equaphase" Circuit, The Freshman 

(J. O. Mesa) ..................... 42 

*Experimental Screen-Grid Receiver, 

An (Charles Thomas) ............. 434 

*Eyes of the Future Air Liner, The 

("Anonymous") .................. 271 

"TT'ACTS About the Fada "Special" 
r Receiver (John F. Rider) ........ 128 

*Fantasy on Sponsored Programs, A 

(John Wallace) ................... 306 

First Rayfoto Transmission, The ....... 348 

*45 kc. A. C. Super-Heterodyne, A 

(Dormand S. Hill) ................ 274 

*Four-Electrode Tube, Applications of 

the (Theodore H. Nakken) ......... 109 

*Four-Tube "Lab" Receiver, The 

(Keith Henney) .................. 423 

*Four-Tube, Screened-Grid Receiver, A 

(McMurdo Silver) ................ 355 

Sound 



PAGE 

Frequency Allocation Outstanding 
Achievement of International Confer- 
ence ............................. 280 

*Freshman "Equa phase" Circuit, The 
(J. O. Mesa) ..................... 42 

From the Manufacturers ............. 174 



46 



of Your Radio Receiver, 
vJMeasuring the (Keith Henney) . . 123 
Growing Political Pressure on the Com- 
mission, The ..................... 347 

TJELIUM ATOM, Radio Enlists 
11 the (Volney G. Mathison) ...... 195 

Here and There ..................... 409 

High-Frequency Channels, Limitations 

to the Use of ...................... 347 

*Hogan, An Interview with J. V. L. 

(Edgar H. Felix) .................. 353 

*How Radio Developments Have Im- 

proved Recording and Reproducing 

(Sylvan Harris) ................... 414 

*How the Cooley "Rayfoto" System 

Works (Austin G. Cooley) ......... 23 

*How the "NR-60" Was Engineered 

(John F. Rider) .................. 299 

How the Radio Beacon Works ......... 108 

How tlte Radio Commission Can Set 

Radio to Rights ................... 105 

*How the "Synchrophase" Seven Was 

Developed (John F. Rider) ......... 232 

*How to Improve Your Old Receiver 

(Edgar H. Felix) .................. 133 

"TMPROVED Aristocrat, The (Arthur 
1 H. Lynch) ...................... 

*Improved Shielded Six (John E. Mc- 

Clure) ........................... 44 

Inside the Radio Industry ............ 281 

Interference, Suppressing Radio (A. T. 

Lawtpn) ................... 48, 217, 379 

""Interview with J. V. L. Hogan, An 

(Edgar H. Felix) .................. 353 

Is Direct Advertising a Service ? ....... 16 

KEY to Recent Radio Articles, A 
(E. G. Shalkhauser) .......... 76, 255 

Kit Shall I Buy? What 66, 170, 257, 330, 393 

*T AB" Receiver, The Four-Tube 
-L' (Keith Henney) ............... 423 

""Laboratory Information Sheets, 
"Radio Broadcast's": 

Acoustics .................. 318 

A. C. Audio-Frequency Ampli- 

fier, An .................. 148 

A. C. Tube Data ........... 58 

Audio Amplification ......... 316 

Audio Amplification, A Prob- 

lem in .................... 448 

B Power Device Character- 

istics ................... 146 

B Power Unil Characteristics 448 
Characteristic! of Speech .... 446 

Circuit Diagram of an A. C. 

Audio Amplifier .......... 148 

Coil Reactance ............. 58 

Comparing the 112, 171, and 

210 Type Tuoes .......... 314 

cx-312 (uc-112) and cx-371 

(ux-171), The ........... 386 



594816 






25 



INDEX Continued 



PAGE 

Data on the ux-222 (cx-322) 384 

Ear, The 318 

Exponential Horn, The 446 

Fading 242 

Filter Choke Coils 387 

Filter Condensers 450 

"Gain" 148 

Grid Bias 387 

How the Plate Circuit Affects 

the Grid Circuit 387 

Inductive Reactance 58 

Loud Speakers 146 

Modulated Oscillator, A 316 

Obtaining Various Voltages 

from a B-Power Unit 60 

112, 171, and 219 Tube Curves 314 
112-A and 171-A Type Tubes, 

The 238 

Operating Vacuum Tubes in 

Parallel 56 

Oscillation Control 150 

R. F. vs. A. F. Amplification 448 

Regulator Tube, The 386 

Resonant Circuits 318 

Selectivity and Sensitivity . . . 384 

Simple Wavemeter, A 386 

Single-Control 150 

Solenoid Coil Data 60 

Speech 150 

Standard and Constant- 
Frequency Stations 238 

Table for Wavelength- 
Frequency Conversion 240 

Testing Receivers 316 

Three-Tube Roberts Reflex. .. 242 
Three-Tube Roberts Reflex, 

The 242 

Transmission Unit, The 60 

Tuning 450 

Type 280 and 281 Tubes. The 450 

Unit of Capacity, The 56 

Wave Traps 240 

Wavelength-Frequency Con- 
version 240 

*Laboratory, "Strays" from the 

228, 310, 427 

"Langley, Ralph H 225 

Limitations to the Use of High-Frequency 

Channels 347 

"Listeners Guests or Customers? 

(John Wallace) 37 

"Listeners' Point of View, The (John 

Wallace) 37, 140. 219, 306, 365, 419 

Listeners Served by Reallocations, 

Rural Radio 279 

*Loftin-White Receiver, An A. C. 

(John F. Rider) 438 

*Loud Speakers 126 

*Loud Speakers and Power Equipment 

22, 373 

*Loud Speakers and Sets, Some New . . 358 

"A/TAKE Your Own Radio Picture 
1VJ. Receiver (Austin G. Cooley) . . . 114 

Manufactured Receivers, "Radio Broad- 
cast's Directory of .... 70, 154, 246, 322, 388 

Manufacturers' Booklets Available 

62, 152, 244, 320, 392 

*March of Radio. The 

14, 105, 198, 278, 346, 406 

*Matching R. F. Coils (F. J. Fox and 
R. F. Shea) 308 

"Measuring the "Gain" of Your Radio 
Receiver (Keith Henney) 123 

*Meters, Kilocycles, or "Channel Num- 
bers"? (Ralph H. Langley) 18 

*Modern Radio Receiver, Refinements 
of the (Edgar H. Felix i 26 

Monopoly Rule the Radio Commission ? 
Does 346 

Month in Radio, The 17, 108, 349 

*Month's New Phonograph Records, 
The 441 

'"Motor-Boating," No (H. O. Ward) 433 

*XTEW A Power Unit, A (Ralph Bar- 350 
1 > clay) 

New Commissioner Appointed 281 

*New Recordings by Radio Favorites 289 
*New "Two-Ten" Power Amplifier, A 

(William Morrison) 138 



PAGE 

News of the Patent Field 16, 108 

*No "Motor-Boating" (H. O. Ward) . . 433 
*"NR-60" Was Engineered, How the 
(John F. Rider) 299 

*PlCTAMONIC" Circuit, The R. G. 
vJ S. (David Grimes) 39 

$100,000 to Improve Broadcasting 107 

"Operating Your Rayfoto Picture Re- 
ceiver (Austin G. Cooley) 296 

*Our Readers Suggest ..." 

35, 131, 213, 293, 363, 421 

*Output, Constant B-Device (G. F. 
Lampkin) 304 

*Output Device? Why the (Keith Hen- 
ney) 294 

* PATENTS: 

Can the Serious Problem of 

Radio Patents Be Settled? 198 
Patent Field, News of the . . . . 16, 108 
Prospects for Patent Pooling . . 15 
Prospects of a Patent Pool, The 198 

*Phonograph Joins the Radio Set, The 

- 112, 206 

*Phonograph Records, The Month's 
New 441 

Picture Broadcasting Becomes a Practical 
Reality 406 

*Picture Broadcasting Station, CJRM, 
Pioneer (Edgar H. Felix) 362 

*Picture Receiver, Make Your Own 
Radio (Austin G. Cooley) 114 

*Picture Receiver, Operating Your 
Rayfoto (Austin G. Cooley) 296 

*Picture Receiver, Why I Installed a 
Cooley (Edgar H. Felix) 215 

Political Pressure on the Commission, 
The Growing 347 

Possibilities of Still Picture Broadcasting 406 

*Power Devices 127 

*Power Equipment, Loud Speakers and 373 

*Power Supply Accessories, Some Re- 
liable Radio 293 

*Po\ver Unit, A New A (Ralph Barclay) 350 

*Programs, A Fantasy on Sponsored 
(John Wallace) 306 

*Programs Going in the Wrong Direc- 
tion? Are (John Wallace) 219 

*Push-Pull Amplification Why? (How- 
ard E. Rhodes) 202 

*Push-Pull Amplifier and B Supply, An 
A. C. (J. E. Coombes) 287 

* DUALITY Five-Tube A. C. Re- 

\,f. ceiver, A (James Millen) 135 

*T~). G. S. "Octamonic" Circuit, The 
JA. (David Grimes) 39 

Radio Beacon Works, How the 108 

"Radio Broadcast's" Directory of 
Manufactured Receivers 

70, 154, 246, 322, 388 

"Radio Broadcast's" Laboratory In- 
formation Sheets (See Laboratory) 

56, 146, 238, 314, 384, 446 

Radio Commission, Action from the .... 15 

Radio Commission Can Set Radio to 
Rights, How the 105 

*Radio Education, University Offerings 
in (Carl Dreher) 339 

Radio Engineering To-day 16 

* Radio Enlists the Helium Atom (Vol- 

ney G. Mathison) 195 

*Radio Favorites, New Recordings by 289 

*Radio Folk You Should Know 225, 286, 440 
*R. F. Amplifier, Designing an (Sylvan 

Harris) 376 

*R. F. Coils, Matching (F. J. Fox and 

R. F. Shea) 308 

Radio Industry, Inside the 281 

"Radio Industry" Standards 107 

"Radio Interference, Suppressing (A. T. 

Lawton) 48, 217, 379 

*Radio Picture Receiver, Make Your 

Own (Austin G. Cooley) 23 

"Radio Receivers for $175 or Less 19 

"Radio Receivers Representing a Wide 

Price Range 302 



PAGE 
*Rayfoto Picture Receiver, Operating 

Your (Austin G. Cooley) 296 

*" Rayfoto" System Works, How the 

Cooley (Austin G. Cooley) 23 

Rayfolo Transmission, The First 348 

*Receivers and Their Chassis, Some 

Fine 226 

Recent Radio Articles, A Key to (E. G. 

Shalkhauser) 76, 255 

*Refinements of the Modern Radio Re- 
ceiver (Edgar H. Felix) 26 

*Roberts, Walter Van B 286 

Rural Radio Listeners Served by Real- 
locations 279 

*QCREENED-GRID Receiver, A 
O Four-Tube (McMurdo Silver) . . 35o 
*Screened-Grid Tube, The (Keith Hen- 
ney) 208 

*Screened-Grid Tube, The (The Labora- 
tory Staff) 282 

*Set Shall I Buy? What (Edgar H. 

Felix) 211 

"Shielded Six, The Improved (John 

E. McClure) 44 

Short-Wave Notes 331 

"Short-Wave Phone and C. W. Trans- 
mitter, A (Kendall Clough) 410 

Short-Wave Spectrum, The Shrinking 407 
*Some Fine Receivers and Their Chassis 226 
"Some New Loud Speakers and Sets 358 
"Some Reliable Radio Power-Supply 

Accessories 293 

South Has Few Stations, Why the 107 

Standards, "Radio Industry" 107 

""Strays" from the Laboratory 228, 310, 427 
"Super-Heterodyne, A 45 kc. A. C. 

(Dormand S. HUD 274 

"Suppressing Radio Interference (A. T. 

Lawton) 48, 217, 379 

Synchronization Schemes, The Com- 
mission Suggests 199 

""Synchrophase" Seven Was De- 
veloped, How the (John F. Rider) . . 232 

"TECHNICAL Radio Problems for 
J- Broadcasters and Others (Carl 
Dreher) 311 

"Television in Europe (William J. Brit- 
tain) 103 

"Testing A and B Power Units (Howard 
E. Rhodes) 443 

Two Stations Cannot Occupy the Same 
Ether Space 348 

""Two-Ten" Power Amplifier, A New 
(William Morrison) 138 

"TTNIVERSITY Offerings in Radio 
U Education (Carl Dreher) 339 

"T 7-ACUUM-TUBE Voltmeter, A 
V (The Laboratory Staff) 221 

TTT'EAF Transmitters, The New 108 

rr "What B Device Shall I Buy? 

(Howard E. Rhodes) 120 

What Broadcasters Want 107 

What Can the Commission Do? 105 

"What is a Good Radio? (Keith Hen- 
ney) 28 

What is the Matter with Radio Advertising 14 
"What's the Trouble with Aircraft 

Radio? ("Anonymous") 11 

What Is the True Broadcasting Situation? 346 
What Kit Shall I Buy? 

66, 170, 257, 330, 393 
What Readers Say About Broadcasting 

Conditions 200 

"What Set Shall I Buy? (Edgar H. 

Felix) 211 

What to Tell the Consumer And Where 107 

Who Buys This Year's Radio Sets ? 279 

"Why I Installed a Cooley Picture Re- 
ceiver (Edgar H. Felix) 215 

"Why the Output Device? (Keith Hen- 
ney) 294 

Why the South Has Few Stations 107 

Will the Radio Industry Do It Again ? . 349 



INDEX Continued 



AUTHORS 



PAGE 



Barclay, Ralph 350 

Bouck, Zeh 416 

Brittain, William J 103 

Brock, F. N 436 

Browning, Glenn H .... 343 

Clough, Kendall . . 410 

Cooley, Austin G 23, 114, 296 

Coombes, J. E 287 

Dreher, Carl 

50, 142, 235, 311, 339, 367, 394, 429 



Felix, Edgar H. 
Fox, F. J 



26, 133, 211, 215, 353, 362 
308 



Grimes, David 39 

Hagerman, Lewis B 413 

Harris, Sylvan 376, 414 

Henney, Keith 28, 123, 208, 294, 360. 423 
Hill, Dormand S 274 

Lampkin, G. F. . 304 

Langley, Ralph H 18 

Lawton, A. T 48, 217, 379 

Lynch, Arthur H 46 

McClure, John E 44 

Mathison, Volney G 195 

Mesa, J. O 42 

Millen, James 33, 135 

Morrison, William 138 



PAGE 
Nakken, Theodore H 109 

Rhodes, Howard E . . . . 30, 120, 202, 443 
Rider, John F 128, 232, 299, 369, 438 

Shalkhauser, E.G.. . . 76, 255 

Shea, R. F 308 

Silver, McMurdo 355 

Smith, Francis Gow 403 

Thomas, Charles 434 

Wallace, John. . . .37, 140, 219, 306, 365, 419 
Ward.H. O 433 

PORTRAITS 
(*Portraits in "The March of Radio") 

*Alexanderson, E. F. W . . 406 



*Bellows, Henry A ... 

Boult Reber 

*Bown, Ralph 

*Butman, Carl H . . . . 
Buttolph, David 

Cason, Bob 

Coates, D. R. P 

Cooley, Austin G 



198 

38 

346 

198 

140 



... 38 
... 362 
.114. 215 



Damrosch, Walter 289, 420 

Dieckmann, Max 104 

*Dillon, John F 107 

Dole, Frank 307 



PAGE 

*Fadden, B. J 201 

Golden, Ernie . . 207 

Goldsmith, Alfred N 346 

Hall, Anita DeWitte . . 38 

Hall, Bob 306 

Hare, Ernest 113 

Hogan, J. V. L 353 

Jones, Billy 113 

Jones, Lester L 440 

Langley, Ralph H 225 

Lindbergh, Charles A 113 

*Marconi, Signora 17 

Mengelberg, Willem 289 

Morecroft, J. H 339 

Palmer, Lester. . 306 

*Pickard, Sam 198 

Roberts, Walter Van B 286 

Shumsky, Oskar 419 

Smith, Francis Gow 402 

Sokoloff , Nikolai 289 

Theremin, Leon 427 

Verbrugghen, Henri 289 

Wynn, Eunice 365 




Copyright, 1928, by 
DOUBLEDAY, DORAN & COMPANY, INC. 







K 







, 

iRefinemerit^in Modern Radio Sets 

' ! ^ ; 

A Directory of Manufactured Receivers 

How the Cooley Rayifoto Picture Recorder^brks 

1 . '. .', . i \. ' -. 

Lets Do AwayWith Meters and Kilocycles 

/ ' ;' V 1 ' ' ' 

iiMtat's the Matter With Aircraft Radio]/ 
What is a Good Radio Set? 1 



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ADDRESS 



RADIO BROADCAST 



NOVEMBER, 1927 



WILLIS KINGSLEY WING, Editor 

KEITH HENNEY EDGAR H. FELIX 

Director of the Laboratory Contributing Editor 



Vol. XII, No. 1 



Cover Design - ' - From a Design by Harvey Hopkins Dunn 
Frontispiece - Proper Radio Equipment on an Airplane 10 
What's the Trouble With Aircraft Radio? .. Anonymous 1 1 
The March of Radio An Editorial Interpretation 14 



What's the Matter With Radio Advertising? 
Action from the Federal Radio Commission 
Prospects for Patent Pooling 
Is Direct Advertising a Service? 



Radio Engineering Today 
News of the Patent Field 
The Month in Radio 



Meters, Kilocycles, or "Channel Numbers"? - Ralph H. Langley 18 

Radio Receivers for $175 or Less 19 

Loud Speakers and Power Equipment - - - 2,2 

How the Cooley "Rayfoto" System Works Austin G. Cooley 23 

Refinements of the Modern Radio Receiver - - Edgar H. Felix 26 

What is a Good Radio? Keith Henney 28 

Do You Own a Battery Operated Set? - - Howard E. Rhodes 30 

Electrifying the Browning-Drake James Millen 33 

Our Readers Suggest. . . . - ' 35 

Listeners Guests or Customers? John Wallace 37 

The Listeners' Point of View 

The R.G.S. "Octamonic" Circuit - - - - David Crimes 39 

The Freshman "Equaphase" Circuit - *-*/. O. Mesa 42 

The Improved Shielded Six - John E. McClure 44 

The Improved Aristocrat Arthur H. Lynch 46 

Suppressing Radio Interference A. T. Lawton 48 

As the Broadcaster Sees It - - - - CarJ Dreher 50 

Putting Freak Broadcasting In Its Place Abstract of Technical Article 

Background Noises Auditorium Acoustics 

"Radio Broadcast's" Laboratory Data Sheets 56 

No. r37 Operating Vacuum Tubes in Parallel No. 141 Obtaining Various Voltages from a 

No. 138 The Unit of Capacity B-Power Unit 

No. r39 Inductive Reactance No. 143 Solenoid Coil Data 

No. 140 Coil Reactance No. 144 The Transmission Unit 

No. 141 A. C. Tube Data 

Manufacturers' Booklets Available 62 

What Kit Shall I Buy? 66 

"Radio Broadcast's" Directory of Manufactured Receivers - - - 70 

A Key to Recent Radio Articles - - - - E. G. Shal1{hauser 76 



AMOT^G OTHER THINGS. . . 

"DOR more reasons than one, the New York Radio Show is 
1- generally accepted as the event which crystallizes interest 
in all things radio. This is written as the show closed and a more 
impressive show we have never seen. "Impressive" from the 
point of view of the exhibits, certainly, but more impressive be- 
cause of the tremendous interest in all things radio demonstrated 
by all sorts and conditions of people who thronged Madison 
Square Garden. Careful observation of the crowds and their 
interest indicated that while the complete sets drew much at- 
tention, the home-assembled receivers built from kits, were 
equally interesting. This definite and lively interest in the 
home-built sets is especially important in view of the pronounce- 
ments of some knowing radio sages who aver that home building 
is seriously on the decline. 

A CTUAL transmission and reception of "still" pictures by 
./V. radio was demonstrated thousands of times during the 
week of the show by Austin G. Cooley who set up a complete 
Cooley "Rayfoto" transmitter and receiver in a special booth 
provided through the courtesy of G. Clayton Irwin, Jr., manager 
of the show. The picture converter or transmitter was set up. 
connected to a small radio transmitter and through a standard 
broadcast receiver, the pictures were received with great 
rapidity and success before the very eyes of eager crowds. The 
simplicity and speed of the receiver astounded those who saw 
the demonstration, and every visitor was eager to know when 
he could build the apparatus and how soon pictures would be 
sent and where he could get information. Experimental picture 
transmissions from various broadcasting stations will be sent 
even before you read these words; complete information on 
how the system works, how to build and operate it appears 
exclusively in this and following issues of RADIO BROADCAST. 
And those who wish to receive printed matter describing 
details of the system should at once address a letter to the 
undersigned who will see that all information is mailed at once. 
The impressive success of the Cooley "Rayfoto" demonstration 
proves beyond all question that a new era has dawned for the 
home experimenter, and to be frank, we are as enthusiastic over 
the possibilities opened up as the keenest of experimenters. 

A WORD about the authors in this issue: the anonymous 
-ti. author of the absorbing leading article is a very well-known 
figure in aviation and radio. Ralph Langley, who explains his 
scheme for numbering broadcast channels, is executive assistant 
to the president, Crosley Radio Corporation. He was until 
recently in charge of receiver design for the General Electric 
Company. Howard E. Rhodes who describes what's new in 
A-power units is one of the able technical staff of this magazine. 
James Millen, who is a consulting engineer and a native of 
Long Island, will shortly desert these parts and settle in Boston. 

TN THE next issue we shall have an important article by T. H. 
1 Nakken on the shielded grid tube indicating what such a tube 
means to American radio .There will be valuable constructional 
articles and a description of the technical features of well known 
manufactured receivers information never published before. 
Austin Cooley will tell how to build a Cooley "Rayfoto" 
receiver facts for which many experimenters are waiting. 

WILLIS KINGSLEY WING. 



Doubleday, Page & Co. 
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OOUBLEDAT, PAGE & COMPACT, Garden Qity, Hew 

Copyright, 1927, in the United States, >fcu>/oundldnd, Great Britain, Canada, and other countries by Doubleday, Page & Company. 

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8 



All rights reserved. 



RADIO BROADCAST ADVERTISER 



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ONE AEROPLANE ON WHICH T 'ROPER <HADIO EQUIPMENT IS USED 

fcf HE Dornier-Napier Whale of Captain F. T. Courtney, originally designed for a flight from London to the United States 
* and return, has a SOO-tvatt Marconi i.c.w. transmitter, using a 200-foot trailing antenna, an eight-tube r.f. amplifier 
ahead of a four-tube super-heterodyne, usable on commercial wavelengths, and a Marconi Bellini-Tosi direction finding 
antenna. The all-metal construction of the ship introduced special receiving problems which had to be solved. Note in the 
lower illustration part of the receiving antenna rising over the motor nascelle. The top photograph shows the radio controls. 
A wind-driven generator supplies power for the transmitter and charges special storage batteries. In case of a forced landing, 
a 40-foot mast can be erected, and the batteries are made to supply current to the motor generator which runs the main set. 

Few airships have been so completely equipped. 



NOVEMBER, 1927 



RADIO BROADCAST 



11 



Whats the TROUBLE with 
Jtmiuft RADIO? 






rHO is to blame for the fact that 
radio communication is not in 
general use in flying? Isittheradio 
engineer? Or can it be shown that the fault 
lies with the airman? Why did not Lind- 
bergh and Chamberlin use radio? Who 
knows in what different manner the fatal 
flight of Nungesser and Coli might have 
ended had there been radio equipment 
aboard the White Bird? What of the Golden 
Eagle and the Miss Doran? Had these 
planes been equipped with radio would 
they have been lost? Probably not. There 
is reason to believe that even though forced 
down, so well would they have been fol- 
lowed by radio watchers on land that they 
might have been quickly found. 

Commander Byrd made good use of 
radio at times in the flight that ended just 
short of Paris. But did he, schooled in the 
Navy and certainly aware of the possibili- 
ties for its use, make the most of his radio? 
One wonders. Why, when approaching the 
French coast, was he unable to learn the 
kind of weather awaiting him at Paris? 
Hegenberger and Maitland were 
able to use their radio equipment but 
a small part of the time on their flight 
to Hawaii. Receiver trouble devel- 
oped soon after leaving the Pacific 
Coast and it was not until they were 
within eight hundred miles of their 
goal that they were able to pick up 
signals again. The preparations for 
their flight were said to have been 
most thorough. The radio must 
surely have been thoroughly tested 
before the take-off, yet it failed 
them in time of need. They had 




planned to fly the course laid down by the 
radio beacon. To do this it was necessary 
to make continuous use of the radio re- 
ceiver. Fortunately, when it failed, they 
were prepared to navigate by better-known 
means. Such was the thoroughness of Army 
Air Corps methods of preparation. 

However, there has been no excuse for 
the lack of radio equipment of some sort 
on all of the trans-oceanic flights. The dis- 
turbance created by the ignition system 
which is almost always offered as an argu- 
ment against it, is not an absolute bar to 
the use of radio. Ignition disturbance has 
no effect on the radio transmitter. Even 
a receiver could have been used to some 
extent in the presence of ignition noise. 
This is particularly true for a plane in which 
the cabin is located some little distance 
from the engine. Furthermore, the receiver 
could have been successfully used while 
passing over vessels at sea. The ship's trans- 
mitter under the circumstances of such 
short range would have pushed signals 



A 7v[O7^TMOLJS" conceals the identity of an individual who is 
cXA excellently qualified to write on the closely related problems of 
the airplane and radio. All we can say is that he is an expert who is 
well \nown in both fields. The author \nows aviation not from a 
swivel-chair vantage point, but from long flying experience and he 
Ifrtows radio from both the practical and distinctly technical angles. 
Too few radio men \now anything about the problems that the aviator 
has to meet, and too few of the airplane jol\ know radio. Certainly 
there is a middle ground on which both may meet and this article is 
the first of several which will discuss this interesting jield. The increas- 
ing fatality list of those attempting stupid and pointless trans-oceanic 
jiights has demonstrated to almost the whole world that long-distance 
/lying must be made safer and surer by every means at our command. 
And through radio will come much of this essential surety. 

THE EDITOR. 



through the ignition disturbance at least 
sufficiently to have given information on 
weather and course. 



RADIO MUST BE USED ON LONG FLIGHTS 



IT WOULD be very interesting to know 



the reasoning which led to a decision to 
leave radio out of the plans for some of 
these flights. Undoubtedly the real reasons 
will not be given to the public. One strongly 
suspects that the lack of ability to handle 
radio on the part of the crew aboard each 
of these planes had a great deal to do with 
the matter. Of course, Lindbergh flew alone 
and could have made little use of any kind 
of radio equipment for that reason. Cham- 
berlin knew little or nothing about radio, 
and it is likely that Levine, his passenger, 
knew less, inexperienced as he was in such 
matters. There is no telling how much Coli 
or Nungesser or Captain Hamilton, the 
British pilot, knew about the use of radio 
equipment. 

None of these flights should have been 
undertaken without radio equipment, 
and a competent radio operator to 
handle it. On some of the flights one 
of the pilots acted as radio operator. 
This did not prove entirely satisfac- 
tory. Hegenberger, who flew with 
Maitland to Hawaii was fairly fa- 
miliar with radio apparatus, but when 
his receivers (there were two aboard) 
became inoperative, he was unable to 
locate the source of trouble. It is 
doubtful if his knowledge of radio 
was sufficient to have enabled him 
to diagnose trouble as a trained radio 
operator could have done. 



12 



RADIO BROADCAST 



NOVEMBER, 1927 



The desire to carry passengers on these 
flights has prevented a good radio operator 
being present. Miss Doran in the Pacific 
flight, and the Princess Lowenstein- 
Waltheim in the Atlantic flight of Captain 
Hamilton, and Philip Payne in Old Glory 
should have been replaced with radio 
operators, and, at least, radio receiving 
equipment. The fact that Brock and Schlee 
flew successfully to England without radio 
is no proof that radio was not needed. 
Redfern carried neither companion nor 
radio. He should not have been permitted 
to leave without both. And his companion 
should have been a good radio man. 

Thus it is seen that some of these fliers 
were unmindful of the value of radio, and 
that others were unable to make the most 
of equipment which they had chosen to 
use. 

Who is to blame that the value of radio 
has been so vastly underestimated in these 
flights? The question 
is important. Upon the 
correctness of the an- 
swer depends in a great 
measure the solution of 
one of the problems which 
at present confronts avia- 
tion. 

WHY AVIATORS DON'T LIKE 
RADIO 

"THERE have been 
1 many discussions on 
this subject between fly- 
ing folk and men interested 
in radio. These discussions 
have usually been of a 
character to which the 
terms " heated," and some- 
times "overheated," could 
justly be applied. Gener- 
ally, the debates ended 
only in disagreement. The 
pilot and the engineer have 
not been brought to the 
same way of thinking. Not 
only have they disagreed 
as to who is to blame for 
the neglect of radio, but the pilot has stren- 
uously objected times without number to 
the use of radio on his plane. 

It is, of course, true that the military 
and naval flier has on occasion done much 
with the equipment designed for him by 
the radio engineer. Very often it was only 
because that flier was a member of an 
organization, in which obedience to an 
order is almost instinctive, that he made 
real use of his equipment. Often, it is true, 
he was pleased with the results of his effort 
and so converts to the cause of radio have 
gradually been made. They are, however, 
all too few. As for the commercial fliers, 
apparently little belief in the need for radio 
exists. One never hears of radio being used 
on their planes. Not even the Air Mail com- 
panies, or our own Post Office department, 
have seen fit to equip mail planes with even 
a receiver with which to receive information 
on the weather. The Air Mail for a time 
carried out experiments with radio but no 



practical or extensive use has yet been 
made of it. 

What has the radio engineer to say for 
himself in the face of this obvious disdain 
on the part of the flier for radio? Were he 
a psychologist it might occur to him that 
the feeling of the pilots about the matter 
might be based on something inherent 
in the flying profession, or in the flier's 
training. Could he put himself in the place 
of the average war-trained flier he would 
remember that in the exciting days of the 
war the urge to fly was the strongest thing 
in his life. It was for that reason that he 
joined the Air Service instead of going into 
some other branch of the Service. That was 
why he worked as he never had worked 
before during preliminary training days at 
ground school. His eyes were always lifted 
to the men in the air. Everything but flying 
was subordinated. Nothing appealed to him 
either at ground school or at the flying 




AT AN EUROPEAN AIRPORT 

Elaborate means of radio communication are required by law on passenger air routes 

in some European countries. The two radio towers at the Tempelhof, Berlin, airport, 

are clearly discernable in this aerial picture 



school to which he was later ordered, as 
strongly as the airplane and flying. Motors, 
navigation, gunnery, photography, radio 
all had to be learned; but he learned them, 
for if they were not learned he would not 
be taught to fly. But flying was the thing 
devil take the rest. Whom did he worship 
the most, his gunnery instructor or his 
radio instructor, or any of the other ground 
instructors? None of these. He worshipped 
the man who taught him how to fly. Usually 
his flying instructor was the biggest man 
on his horizon. His radio instructor was 
usually a non-flier, "Keewee" being the 
term contemptuously applied to any ground 
officer of the Air Service. Usually this man 
made no impression, or a poor one at the 
most. He often stood between the cadet 
and his flying goal. For all who would fly 
must, in addition to many other things, 
learn to send and receive radio signals. If 
he could not pass the speed test he could 
not fly. That was the regulation, and many 



a good man was " shot down " by the elusive 
da-dit-da before he ever had a chance to 
learn to fly, and was accordingly sent away 
from flying school. At the advanced flying 
school came practice with actual transmit- 
ting and receiving of signals while in the air. 
This was usually even more boring than 
the practice in the code room. Generally, 
the radio failed to function. Anyhow, who 
wanted to sit in the rear cockpit of a ship 
which was being flown by someone else 
and fiddle with knobs and dials and try to 
pick up the faint signals bravely endeavor- 
ing to penetrate the noise and roar of the 
motor and the disturbance created by the 
ignition system? 

Thus was built up all through the fliers' 
training, a genuine dislike for radio. As so 
many of the present fliers were war-trained, 
it is little to be wondered at that radio still 
has no appeal for them, and that the aver- 
age flier has but little faith in it. A man was 
generally judged by his 
ability to handle his 
"ship." If he was clever 
with radio, providing he 
was able to fly, he was 
forgiven by his fellows. 

Experienced fliers are 
among the most conserv- 
ative of men, strange as 
that may seem. Little do 
they relish change or inno- 
vation. They have been 
flying through all kinds 
of weather and over all 
kinds of country without 
the use of radio. Why 
change now? Radio is just 
another thing to worry 
about. It probably won't 
work anyway, and the 
receivers in the helmet 
hurt your ears and you 
can't hear your motor. 
So poor old radio goes for 
consolation to the amateur 
who has been such a good 
friend all these years. All 
of which the radio engi- 
neer has probably not realized. 

TECHNICAL PROBLEMS IN THE PLANE 

IN ADDITION to the obstacles formed 
* by the fliers' attitude, there have been 
many technical difficulties to overcome. 
Chief of these is the interference caused by 
the ignition system of the airplane engine. 
This has been a most serious obstacle and 
has not been completely overcome. It is 
true that, by completely shielding the 
ignition system, the troublesome noise can 
be reduced to a point where very satisfac- 
tory reception in an airplane is attained, but 
such shielding is difficult to install and even 
more difficult to maintain. 

How is a motor shielded to reduce this 
interference? How does the ignition system 
of a motor produce interfering noises in a 
radio receiver? 

The ignition system consists of a highl- 
and low-tension side. The low-tension side 
consists of everything from the switches to 



NOVEMBER, 1927 



WHAT'S THE TROUBLE WITH AIRCRAFT RADIO? 



13 



the low-voltage side of the magneto in mag- 
neto ignition; and everything from the bat- 
tery, including switches, generator, meters, 
voltage regulator, and distributors in the 
battery type of ignition. In the high-tension 
side we have everything from the high- 
tension side of the magneto in the first type 
of ignition, and from the distributors in the 
second type, down to the spark plugs. In 
these systems every make and break con- 
tact, as in voltage-regulator relay or dis- 
tributor, produces a disturbance each time 
the circuit is opened or closed, which should 
be regular and very frequent, otherwise 
the pilot has something much more serious 
to worry about than the QRM from his 
ignition. The spark plug has not been men- 
tioned in detail yet. Usually there are two of 
these little short-wave transmitters in each 
cylinder of the motor. The average air- 
plane engine runs at speeds of from 1400 
to 1800 revolutions per minute. This means 
that in an eight-cylinder, four-stroke-cycle 
engine, equipped with but one spark plug 
per cylinder, there will be at 1500 r.p.m., 
six thousand sparks per minute, or one 
hundred sparks per second. This produces 
a noise in a radio receiver which resembles 
the noise produced by a stream of shot on 
a loose tin roof. Oscillograms of this QRM 
indicate that part of the noise is due to 
induction, just as the "click" heard in 
a receiver when an electric light switch 
nearby is opened or closed, is caused by the 
change in current. The rest of the noise is 
produced by the oscillating spark in the 
gap in the spark plug itself. This is a true 
electro-magnetic disturbance of a definite 
wavelength. Apparently, then, it should be 
easy to reduce this interference by means of 
a short-wave trap; and so it should, but due 
to the difference in the constants of these 
small oscillating systems, the use of wave 
traps has not proved very satisfactory. Up 
to the present time the most satisfactory 
method of freeing the receiver of this an- 
noying disturbance is by shielding the 
whole ignition system. 

Completely shielding the ignition system 
requires that every wire and electric device 
about the whole plane which carries current 
be covered with an electric shield. This is 
usually a braided copper sleeve, slipped 
over the wire, or a metal container for such 
devices as regulators, distributors, and 
switches. This shield must be connected to 
the ground of the plane. The ground of an 
airplane consists of all the metallic parts, 
such as the motor, brace wires, cables 
and fittings. If you have a few inches of 
frayed shielding it will cause all the noise to 
come right back to the receiver. Shielding 
produces a hazard, the danger of which 
may be readily realized. If there is faulty 
insulation anywhere in the system, the 
vital ignition current will jump through to 
the ground and out goes part or all of the 
ignition, depending upon where the break 
occurs, and, it is needless to say, down 
comes the plane, to make as safe a landing 
as the pilot can. It would appear that the 
solution of this problem is to use nothing 
but the best of insulation. This is more diffi- 



cult than it sounds. When a high-tension 
lead is shielded a corona discharge takes 
place through the insulation to the 
grounded shield. The corona produces a 
chemical change in insulation and it no 
longer insulates, the engine ceases to 
"percolate," and the aviator to "aviate." 

Now, the pilot knows all this and his 
feeling for radio has increased in warmth, 
but not in a direction the radio engineer 
would like to see. The old feud still exists. 
The pilot says the engineer loads his plane 
with hazardous equipment, and the en- 
gineer says the pilot is too fussy about what 
happens to him. 

THE FUTURE WORK FOR ALL 

AND so it stands, until the necessity 
for radio communication between the 
air and the ground is made apparent to all 
concerned with flying. That this necessity 
exists there is no doubt in the minds of 
many besides the radio engineer, but now 
the demand for radio is insufficient to in- 
duce very much research on these problems. 
Such problems can be and are, of course, 
being worked on in laboratpries. However, 
there is a definite limit to what can be done 
in a laboratory on the ground. The condi- 
tions existing in a plane the vibration, 
the noise of wind and motor and ignition, 
cannot be adequately reproduced in a 
laboratory; nor can engineers conceive of 
the conditions except by repeatedly ex- 
periencing them in test flights. What I am 
driving at is this. There should be a labora- 
tory in which the ground and air work is 
connected and closely related. The engineer 
should be placed in a position not only to 
see the problem as the flier sees it, but both 
flier and engineer should be encouraged to 
work together. Confidence in the ability 
and work of the engineer will then come to 
the flier. Better radio sets will be built, 
and let us hope that they will be built as a 



part of the plane and not tacked on an 
afterthought. Airplane designers will make 
provisions for these sets and the power re- 
quired to operate them. Then, and then 
only, will pilots want radio, and make good 
use of what they get. 

Before passenger carrying air lines are 
permitted to operate either in this country 
or on trans-oceanic flights, this matter of 
radio should be included in the regulations 
covering the safety and inspection of the 
planes. The Department of Commerce 
should make regulations to fit the needs of 
the moment. Because commercial aviation 
is in its growing stage, the regulations 
should be fairly elastic. But before passen- 
gers are permitted to risk their lives, regula- 
tions regarding suitable radio equipment 
and personnel to operate it should be laid 
down. These should cover all long flights, 
whether over water or land. By long flights 
is meant anything over 500 miles. 

The radio beacon has had but a very 
short test outside of the Air Corps ex- 
perimental tests. But it is apparent even 
on such short trial that regular flights over 
long distances of water should not be 
thought of without contemplating the use 
of such a beacon. For regular passenger 
routes over land, the beacon should be de- 
pended upon at least for night flying. How- 
ever, the story of this beacon and its possi- 
bilities is too long to include here. 

As in so many other things, practice and 
test are essential to development, and this 
is no less true of radio on aircraft. The more 
use made of it the more experience gained. 
Radio has a very definite and important 
place in aviation, and it is only to be re- 
gretted that use has not been made of it on 
all transatlantic and transpacific flights. 
It is likely that the unsuccessful flights 
would not have had so tragic an ending, 
had radio played the part that it must come 
to play in the future of aviation. 




WHEN RADIO WAS NO MORE THAN A DREAM 

King Edward VII receives a lesson in aeronautics at the hands of Wilbur Wright. Planes of ten years 
hence, equipped with powerful radio transmitters and receivers, will probably be as much in advance 
of present day design as are the planes of to-day as compared to this fragile looking craft of Wright's 



NFVVS AND INI1.HPKKTATIQN OF" ('.IIUUKNT UAhlQ KVKIM I S 



What is the Matter With Radio Advertising? 



FROM time to time, trade associa- 
tions and better business bureaus 
formulate codes of ethics for the 
guidance of writers of radio advertisements. 
These codes aim to curb exaggerated claims 
as to long distance reception, quality of 
tone and other excesses so freely used in 
radio announcements. 

The beautifully worded hyperboles, char- 
acterizing modern advertising, have re- 
ceived such spirited attacks recently, that 
we may look forward to saner and more 
informative advertising copy. So great is 
public interest that a book on this subject, 
Your Money's Worth, is threatening to 
become a best seller. Radio advertising 
receives its share of scathing criticism from 
these authors who leave no one unscathed. 

Imagination at least is lacking when 
an entire industry depends upon a few 
standardized general appeals to sell its 
products to the public. If the advertising is 
to be believed, all receiving sets possess 
unbelievable selectivity, marvelous sensi- 
tiveness and magnificent tone quality, re- 
gardless of pjice. Rarely does any enlighten- 
ing information appear in a radio advertise- 
ment by which a prospective purchaser may 
judge the superiority of one receiver over 
another. Magical phrases are concocted, 
playing upon the ignorance of the non- 
technical, to suggest fancied engineering 
superiority. The uninitiate must be 
guided by such medicine-man hokum 
as "utilizing the new intra-paralytic 
principle of interference submer- 
gence," "delightful tone quality ob- 
tained with the mastertonic sliding 
trombone transformers," or "securing 
magical selectivity by the matched 
prismatic quartz inductances." 

Aside from such senseless and 
meaningless technical appeals, most 
radio advertising confines itself to 
generalized boasts. The same charge 
may be made not only against the 
advertising of radio sets, but that of 
automobiles, iceless refrigerators, and 
any mechanical or electrical product. 
The readers of RADIO BROADCAST 
frequently demand that some com- 
parative technical tests be made to 
form a basis of judging the relative 
qualities of sets. 

We have given considerable 
thought to this problem and we 
would unhesitatingly publish com- 
parative information, could we dis- 
cover a method of making compara- 
tive tests which would not involve 
the human element and which would 
be a real test of merit, taking into 



consideration all of the factors which con- 
tribute to the desirability of a radio re- 
ceiver. 

Take, for example, the factor of gain in 
the radio-frequency amplifier. We may im- 
press a standard modulated signal from an 
oscillator upon a receiver and measure the 
resultant fluctuations in plate current of 
the detector circuit, thus giving an evalua- 
tion in the over-all gain of the radio-fre- 
quency amplifier. We may also obtain a 
selectivity curve for each receiver which 
gives a fair index to that quality. Further- 
more, given an adjustable audio frequency 
oscillator, with which to modulate the in- 
coming test signal, we can determine with 
a fair degree of accuracy the tonal range 
and characteristics of the audio frequency 
amplifier. These three tests would give an 
index to the three major qualities of a re- 
ceiving set, namely its sensitiveness, selec- 
tivity and fidelity. 

Unfortunately, carrying out such tests is 
far from simple. Most receivers have a gain 
control in the radio-frequency amplifier 
system which greatly complicates labora- 
tory tests as a means of comparing receiving 
sets. Testing a five-tube receiver, the gain 
might well be adjusted as high as possible, 
so that it would show maximum amplifica- 
tion per stage. However, when so adjusted, 
it is likelv to show more than normal dis- 




> 



SENATORE MARCONI TESTING BEAM TRANSMISSION 

The inter-continental beam transmitters of the Marconi Com- 
pany, now in operation, resulted from a long series of tests. 1 his 



illustration shows Senatore Marconi testing a short-wave trans- 
mitter from a boat on a lake at Livorno, Italy, in 1916 



tortion in its audio-frequency amplifier. 
On the other hand, more conservative ad- 
justment of the radio frequency gain would 
handicap its sensitivity rating, although it 
might improve its showing with respect to 
tone quality. Five engineers could test a 
number of receivers and secure entirely 
different results. 

If a sufficient number of test conditions 
are fixed so that the element of adjustment 
would be minimized, some receiving sets 
would be unduly handicapped by the test 
conditions in one respect or another. Con- 
sequently, laboratory comparisons, with 
the test methods we now have available, 
do not, for the present at least, seem to 
offer a means of supplanting generalities in 
radio advertising. But we may look forward 
to developments in this direction, as our 
experience with laboratory measurements 
of sets increases. 

Another possible method of making ad- 
vertising copy more informative is to give 
a few outstanding facts regarding a re- 
ceiver, such as number of tubes, number of 
controls, and other specifications. But the 
number of tubes in a receiver is hardly a 
guide to its efficiency. There are ten-tube 
receivers which give no better results than 
other six-tube sets. The writer, for instance, 
has a four-tube receiving set with a 210 
tube in the output, which he would confi- 
dently enter in any contest for sensi- 
tiveness, selectivity and tone quality. 
But, as a commercial product, it is 
practically useless. It takes an ex- 
pert to tune the set and the filters, 
chokes and by-pass condensers, which 
are a part of it, would not fit into two 
set cabinets of normal dimensions. 
So the listing of specifications is 
hardly a panacea for indefiniteness 
in radio advertising. 

What remains to assist the honest 
advertiser in preparing truly inform- 
ative copy? If we rule out bunk, 
generalities and specifications, of 
what may the set manufacturer speak 
without being frowned upon? Only 
three general points suggest them- 
selves outward appearance, price, 
and reputation, the same factors 
which the automobile industry has 
found successful as selling appeals. 

Another possibility is to consider 
some one, simple, technical detail 
the thickness of shielding, the 
strength and rigidity of the chassis, 
or the accuracy with which tuning 
circuits are matched as an indica- 
tion of the skill and care displayed 
throughout the whole receiver. Such 



NOVEMBER, 



MORE ABOUT PATENT CONTROVERSY 



15 



a pojfcy has advantages, being informative, 
specific, interesting, and, above all, based 
on facts instead of on generalities. 

Prestige and reputation are the product 
of years of successful manufacture, and, 
consequently, production figures and value 
of sets sold by a manufacturer are a founda- 
tion of fact by which an old established 
manufacturer may distinguish himself from 
others. 

A method, which has been successful in 
other fields, is to "sell" the engineer who 
designs the product. Certain companies 
have engineering and research staffs of 
acknowledged competence and reputation, 
whose designs are worthy of great public 
confidence. 

A thorough and detailed study of the 
radio receiver and those who build it, on 
the part of the advertising copy writer, is 
the best preparation for writing advertising 
which features facts rather than fancy. 

Action from the Radio Commission 

THE Federal Radio Commission has 
begun suit against station KWKH, 
which it charges with the misdeed of 
using three times the power permitted by 
its license, for forty successive days. As a 
result, KWKH is liable to fines aggregating 
$20,000 at the rate of $500 a violation. 
If the Commission has a good case and wins 
out in the courts, it will certainly gain wide 
respect. The numerous violations of the 
Commission's regulation as to maintenance 
of assigned frequencies are likewise subject 
to fines of five hundred dollars a day. 
Certain stations frequently wander as much 
as ten kilocycles from their channels. The 
former WSOM, for example, was found at 
different times, within eight days, 24.8, 
23.9, 12.5 and 1 6. i kc. from its assigned 
channel. 
The Commission, in a public statement, 



threatened to eliminate about twenty-five 
of the most flagrant wavelength wobblers 
but, as usual, grew softhearted in the end 
and gave them additional grace. Hetero- 
dyning is far too widespread to make listen- 
ing to any but relatively nearby stations 
any very great pleasure. 

The Commission's claim, however, that 
practically all heterodyning is due to fre- 
quency wobbling is not entirely founded on 
fact. There are altogether too many assign- 
ments of stations to the same frequency 
whose carrier waves are bound to create 
interference. The clearest broadcasting 
channels as a matter of fact, are at this 
time the higher frequencies between 1250 
and i 500 kc. On these frequencies, we find 
mostly low-powered stations which do not 
interfere with each other. 

The numerous hearings held in Washing- 
ton, upon demand of some of the 'stations 
now assigned to these superior channels, 
are based on the fallacious superstition that 
the lower frequencies are the most desirable. 
At one time, when the lower frequencies 
were reserved for the better stations, while 
as many as twenty and thirty low- and 
medium-powered stations were huddled on 
the lower end of the broadcast band, the 
ambition to leave the higher frequencies 
was justified. Although conditions have 
changed, prejudice against the higher fre- 
quencies persists. 

Mr. May, seeking a lower frequency 
for his advertising station, KMA, for exam- 
ple, testified before the Commission that 
it was a well known fact among radio en- 
gineers that the channels below 350 meters 
were "practically no good for broadcasting 
purposes," although, as an expert brought 
out, KDKA, KOA, WBBM, WOK, and numerous 
other stations, occupying these allegedly 
unsatisfactory frequencies, have built up 
nationwide audiences. 

The claim that stations do not "get out" 



on the very high frequencies is made be- 
cause the public is not accustomed to look- 
ing for its programs on these channels. 
There are too few worthwhile stations 
using them. Why not assign a few really 
good stations to the higher frequencies, so 
as to distribute the public's attention 
throughout the broadcast band? 

Prospects for Patent Pooling 

THE Radio Manufacturers' Associa- 
tion is looking into the matter of 
patent pooling and seeking to in- 
augurate a system of cross-licensing in the 
same manner that the automobile industry 
accomplished this through the National 
Automobile Chamber of Commerce. There 
is one great difference, however, in the 
radio situation and that lies in the fact that 
a single group has already concentrated 
most of the patents in its own hands and 
consequently no one has much to offer it 
for bargaining purposes. 

We learn of the formation of a Radio 
Protective Association in Chicago with the 
object of battling against "radio monop- 
oly" which, say the sponsors for the new 
organization, "will be taken to Congress, 
to the Department of Justice and to the 
Courts." 

No matter how much outsiders may pro- 
test, there is no question about the fact 
that the Radio Corporation of America 
has in its hands most of the essential pa- 
tents to the 'manufacture of the radio 
receiver and it is not at the mercy of any 
outside group. A patent is an entirely legal 
monopoly created by legislation in accord- 
ance with provisions in the Constitution 
of the United States. Furthermore, the 
Radio Corporation is extending licenses to 
competing companies on what appears to 
be a fair basis. A rather large minimum 
royalty guarantee is required of the set 





TESTING "BEAM" TRANSMISSION IN 1916 

Senatore Marconi's principal assistant in the development of the short- England with Canada, India, Australia and South America, and the 

wave "beam" is C. S. Franklin who is here shown on the lake at Livorno, New York-London link will shortly be opened. C. S. Franklin, Senatore 

Italy, testing a short-wave receiver with transmissions from the parabolic Marconi's chief research engineer, famed for his work in developing the 

reflector shown in the accompanying photograph. (Right) The "beam" "beam" method is shown here operating the beam transmitter with its. 

system of short-wave communication has already satisfactorily linked parabolic reflector from the shore of the lake at Livorno 



16 



RADIO BROADCAST 



NOVEMBER, 1927 



maker; said to be $100,000 a year, which 
effectively throttles the small producer. 
Under the patent law, a patent holder has 
full rights to deny the issuance of licenses 
to anyone he chooses and, therefore, unless 
the legal attitude of the patent law is 
completely reversed, the R.C.A. is entirely 
within its rights. 

The object of the patent law is to assure 
that inventors are encouraged and properly 
rewarded. Times have changed and inven- 
tion is much less a product of individual 
genius than it is the marshalling of many 
minds, research facilities and laboratory 
experience. The reward, instead of going 
to individual inventors and their backers, 
now goes to large corporations which make 
it possible for the complex invention of this 
day to be made. 

The major purpose of the patent is thus 
fulfilled, both under modern conditions 
and under those which obtained in 
the past. We may add a new inter- 
pretation in that the patent mo- 
nopoly shall not be used in restraint 
of competition and ' compel patent 
holders to extend licenses to all those 
willing to pay just license fees. This 
plan is followed in Canada. But such 
a course in this country would be a 
new situation, a reversal of prece- 
dents. It would require new legisla- 
tion. A possible and, indeed, probable 
solution of the present radio situation 
is that the Radio Corporation will 
extend licenses to smaller concerns on 
a smaller minimum guarantee, but 
upon a higher percentage of royalties 
than it extends to those guaranteeing 
$100,000 a year. 

The radio industry is suffering from 
the existence of too many incompe- 
tent small manufacturers which are 
bound, in time, to be eliminated by 
natural economic processes. Hasten- 
ing their passing by patent pressure 
is a painful but effective method 
which, however, reacts unfavorably 
against those exerting it. But, what- 
ever the considerations animating 
the policy, the legality of the R. C. A.'s 
present patent course does not appear to 
be open to question. 

Is Direct Advertising a Service? 

A NUMBER of the direct advertising 
stations have appeared before the 
Commission, claiming great losses 
of audience and service range because of 
their high frequency assignments. Mr. 
May, speaking for KMA, recently spent 
three and a half hours on the stand, a 
record for a single witness before the Com- 
mission to date, to prove himself the most 
popular announcer in the United States 
and his station the greatest service to hu- 
manity of any station in the corn belt. 
450,000 people wrote him during the first 
seven months of the year, a larger number 
than practically any but one or two key 
chain stations can claim. 
On the other hand, every questionnaire, 



not specially circulated by the stations 
themselves or by farm papers, indicate the 
wholehearted public condemnation of di- 
rect advertising by radio. RADIO BROAD- 
CAST'S questionnaire, in which 10,886 ex- 
pressions of approval and disapproval were 
made, found KFNF the most unpopular 
broadcasting station in the country, 18.8 
per cent, of the audience demanding its 
removal. Considering the fact that those 
who answered this questionnaire were dis- 
tributed all over the United States, this 
seems to represent about 100 per cent, of 
the listeners within the annoyance range of 
this station. WJAZ won the disapproval of 
1 5 per cent, of the listeners, most of this 
vote being a spite vote because WJAZ upset 
the Radio Act of 1912, rather than because 
of present day program unpopularity; while 
KMA came out third with condemnation 
from 13 per cent, of those answering. 




SIGNORA MARCONI 

The illustration shows the wife of the noted Italian with the 

radio receiver fitted up for her use in their palace in Rome. 

Signora Marconi was formerly the Countess Maria Cristina 

Bezzi Scali 



However, 450,000 people do not write 
a station for nothing. There is no question 
but that there is a field for the local broad- 
casting station in the serviceof the small local 
merchant. The public, however, resents be- 
ing sold harness, glue, tires, and laundry ser- 
vice in the guise of entertainment. The mail 
order buyer in the rural district is about the 
only group which responds. Evidently, in 
spite of the harsh dislike which we have of 
the direct advertising stations, we must con- 
fess that they have an audience and, as such, 
deserve consideration, but only in propor- 
tion to the importance of that audience. 



Radio Engineering To-day 

ALPH H. LANGLEY of the Crosley 
Company writes us at some length 
in comment on D. A. Johnson's 
criticism of radio engineers, which we 
headed, some months ago, "There Are no 
Radio Engineers." Mr. Langley points out 



R 



the excellent progress made in building up 
technical knowledge through the work of 
the Institute of Radio Engineers and de- 
scribes what is being done in the way of 
standardizing symbols and terms and 
measurements. Mr. Langley says: 

No branch of engineering can become an exact 
science, until its methods of measurement have 
been developed and standardized. But the pro- 
gress which radio science has made in this 
respect during the past three years is remark- 
able and gratifying. It is now possible to pre- 
dict with reasonable accuracy the field strength 
which will be delivered at any receiving point 
by any transmitter. The characteristics of the 
transmitted wave are accurately measurable. 
The field strength necessary to produce a 
given output voltage on any receiver can be 
determined from the measured characteristics 
of the receiver and of the antenna. The ability 
of the receiver to exclude undesired signals 
and its acoustic performance, as well as that of 
the loud speaker, are. also subject to pre- 
cise measurement. Transmitters have been 
metered and their characteristics known 
for many years. Thus every part of the 
broadcast mechanism has yielded to pre- 
cise determination. 

As a mushroom and a boom in- 
dustry, radio was certainly unscien- 
tific. But progress has been made. 
An inspection of the twenty leading 
manufacturers' plants would quickly 
convince Mr. Johnson that the design 
and manufacture of the radio product 
is a precision task of the highest order, 
performed to the most rigid standards. 

News of the Patent Field 

A RECENT licensee under Radio Cor- 
poration patents, and probably the 
most important from the standpoint of 
royalties to be paid, is the Atwater Kent 
Manufacturing Company. This brings the 
total number of licensees to twenty-three, 
including some of the principal manu- 
facturers of the industry. Within the pale 
are a number of companies who must 
produce considerably more sets and 
do a much larger share of the total radio 
business this year than last if they are 
to earn their royalty guarantee. On the other 
hand, there are still one or two large manufactur- 
ers outside the pale who have not yet indicated 
any intention or desire to obtain a license. No one 
knows yet just what their course will be. One 
possibility is an attempt to build receiving sets 
completely evading infringement of Radio Cor- 
poration patents. There are engineers who con- 
tend that this is not impossible, although really 
more than this result must be achieved. The sets 
must not only avoid patent difficulties, but must 
be as inexpensive to manufacture and as efficient 
so far as results are concerned as receiving sets 
made under Radio Corporation licenses. That 
is no small problem, f t f Heins and Bolet ac- 
cepted a consent decree in a case brought by the 
Westinghouse Company under Armstrong, 
Fessenden and Vreeland patents, f I f The de- 
cree against the Claremont Machine Company, 
secured by the C. F. Mueller Company, for a 
machine for folding noodles was sustained, Ml 
A decision rendered in the U. S. Circuit Court al 
Philadelphia upheld the Lektophone patent 
1,271,529, declaring that Lumiere's invention 
does not anticipate Hopkins and that the de- 



NOVEMBER, 1927 



BRIEF RADIO NEWS AND COMMENT 



17 



fendants' device, employing a flexible rubber 
liaison member, held in place by a rigid frame 
ind covered by an ornamental hood, is an in- 
fringing device. I M The following sets are now 
licensed under R. C. A. patents: Zenith, Splitdorf, 
Stromberg-Carlson,Bosch,Crosley,All-American, 
Freed-Eisemann, Howard, King, Fada, Federal, 
Murdock, Freshman, Amrad, Steinite, Gilfillan, 
Day-Fan, Bremer-Tully, Atwater Kent, Federal- 
Brandes, A. H. Grebe, Pfansteihl and United 
States Electric (Apex, Case, Slagle, Workrite, 
and Sentinel). 



The Month In Radio 



THE evolution of marine radio communica- 
tion was recently described by T. M. 
Stevens, General Superintendent of the 
Marine Department of the R. C. A. Broadcast- 
ing considerably hastened the adoption of a 
continuous wave transmission on a new series of 
channels, greatly mitigating interference with 
broadcasting. In 1922, there were twelve spark 
stations, using principally the waves of 450 and 
600 meters, along the coast from Cape May to 
Bar Harbor. Both on account of congestion and 
because of the protests of broadcast listeners, 
seven of these twenty spark stations are now 
closed down and the remainder have been re- 
placed by more efficient vacuum tube transmit- 
ters. Three hundred ship spark transmitters have 
also been converted into modified tube transmit- 
ters so that they no longer interfere with broad- 
casting programs. 

A few small independent companies are still 
compelled to use spark transmitters, while many 
foreign ships with spark transmitters are still 
working in a manner to interfere with broadcast 
listening. It is understood that the independent 
radio companies, operating spark stations, are 
experiencing difficulty in obtaining properly 
licensed vacuum tube transmitting equipment. 
The foreign ship interference will probably be 
tackled by the International Conference at 
Washington. Under the circumstances, spark in- 
terference with radio programs is likely to be a 
thing of the past within two or three years, and, 
possibly sixty to eighty per cent, of the inter- 
ference is already eliminated. ? f f Things have 
changed for ship operators since the writer 
pounded the key some twelve years ago. In those 
days, the emolument was sixteen dollars a month 
and now it averages a hundred. Considering that 
the work is generally pleasant and practically 
all expenses are paid, the radio operator's lot is 
one to be envied, when compared with that of 
the clerk with his dull routine and the artisan 
with his arduous and confining tasks. The radio 
operator's principal complaint, as we have 
gathered from interviewing a few, is that once 
senior operator on a desirable ship, contact with 
superiors is so limited that the opportunities for 
advancement are practically nil. Nevertheless, 
most of the executives of commercial radio com- 
panies were once "brass pounders." There is no 
employment more romantic, responsible and 
broadening than that of radio operating for the 
young enthusiast, seeking a career of adventure 
and promise. Iff The listeners of KFWO, an 
efficient little 25O-watter at Avalon, owned by 
Lawrence Mott of short-wave fame, have been 
receiving play-by-play reports of the games 
played in Chicago by the Cubs. Why this station 
should go so far afield to present its listeners with 
this feature is explained by the fact that Mr. 
William Wrigley, Jr., is so interested in the doings 
of the Cubs that, while he summered at Catalina. 
play-by-play reports were sent him by telegraph. 



Mr. Mott suggested to Mr. Wrigley that these 
play-by-play reports be diverted to KFWO and 
then broadcast. Colonel Green has a rival! f f I 
The Egyptian government plans to erect a 
broadcasting station. There are already three 
thousand sets in operation which, to receive the 
principal European programs, must be highly 
sensitive. Eighty-five per cent, of the population 
of Egypt lives within 150 miles of Cairo and 
hence a single station can greatly stimulate a 
market which American manufacturers may do 
their share in supplying, f f f Any listeners, hear- 
ing broadcasting station SOL, have been victims 
of a slight error which is excusable, due to the 
distance involved. They are doubtless hearing 
station XOL, operated by the Tientsin Govern- 
ment in China. Its power is 500 watts and it 
uses a wavelength of 480 meters. A special license 
is required from the Chinese government to act 
as an importer of radio sets and one American 
Company has taken advantage of this privilege 
by conforming with the regulation, f ( t A beam 
station, another link in the Marconi worldwide 
service, has recently been opened for commercial 
use at Johannesburg, South Africa, f ? ? WLW, 
using its short wavelength, supplied an Austral- 
asian program recently, enjoyed by listeners of 
2 FC, Sydney, Australia, and I YZ, Auckland, 
New Zealand. America is the largest exporter 
of broadcasting programs in the world, f f If 
The interference problems of Australia are caus- 
ing distressing controversy. A new 1 5-kw. broad- 
caster is to open at Wellington on 420 meters. 
What worries the Australians is if Sydney on 440 
and Adelaide on 400 meters will not suffer serious 
interference. Cautious fellows these Australians! 
fit JOAK, Tokio, already frequently heard on 
the Pacific Coast on its thousand watts, is to go 
on 40,000 watts, which should certainly bring 
it within range of a good part of the United 
States during early morning, midwinter hours. 
It won't be long now before a few American 
broadcasters will have to close down because of 
foreign interference. Iff There are 206,334 
listeners in Australia, duly licensed and paying 
license fees, f f ? The British Broadcasting 
Corporation issued a statement recently that it 
had discovered the advantages of rating stations 
in terms of kilocycles rather than meters. The 
advantages of the kilocycle rating have become 
obvious to the American listener and have been 
used in this magazine since August, 1925. In 
talking to the members of the Federal Radio 
Commission, we have been pleased to notice 
that, though at the first the word "wavelength" 



was rather frequently in the conversation, it 
did not take long for the Commission to adopt 
"frequency" as the only practical term to desig- 
nate the radiation of a broadcasting station. 

WHO REPRESENTS THE LISTENER? 

OUR editorial some months ago, entitled 
"Where Are the Listeners' Organizations?" 
has brought forward a good deal of correspond- 
ence from ambitious would-be executive secre- 
taries, disillusioned leaders who have attempted 
to form local organizations and readers request- 
ing RADIO BROADCAST to sponsor such an organ- 
ization. A number have expressed the opinion 
that listener organizations would be more of a 
nuisance than an aid to broadcasting. W. W. 
Waltz, for example, writes that, although in his 
area wjz, WEAF, WGY and KDKA are the obvious 
program leaders, there is a certain advertising 
station which any Philadelphia listener will re- 
cognize, "whose sole idea is to sell every ampere 
that can be forced off of their antenna. There is 
no use in trying to describe the junk they broad- 
cast. Everything from near-dirty stories to 
grand opera selections by the most horrible or- 
chestras in existence. One complaint after an- 
other has been made, officially and otherwise, in 
regard to the manner of operation of this station. 
Their equipment is modern, but it is adjusted 
to give a wave like a spark set. And believe it or 
not is the most popular station in the city!" 
The conclusion to be drawn is that no organiza- 
tion can be truly representative of listener tastes. 

HOW LONG, OH LORD, HOW LONG? 

WE TAKE a special delight in reminding the 
authors of publicity statements boasting 
of revolutionary inventions, of the prior discov- 
ery and origin of these same inventions, in the 
hope that more care and conservatism may be 
displayed, as time goes on, by the publicity ro- 
mance writers. We note that Mr. C. Francis 
Jenkins, who has spent many years in research in 
telephotography, announces the development of 
radio guiding channels to keep aviators on a 
definite course and of a receiving set giving visual 
indication of deviation from the guiding course. 
The former has already been widely used exper- 
imentally, especially by the Navy Department, 
and is a well known invention. The visual indica- 
tor is not so widely used, although its develop- 
ment in direction-finding apparatus was recorded 
in these columns several months ago. About 
twenty-five ships on the Great Lakes are already 
equipped with the visual direction indicator. 




FADING TESTS AT MELBOURNE, AUSTRALIA 

Station 3 LO at Melbourne has made a gift to the University of Melbourne for research on the causes 

of radio fading. R. O. Cherry, working under Professor Laby of the University, is here seen calibrating 

the portable receiver for measuring signal intensities. The set is carried in an automobile 



METERS, KILOCYCLES, OR "CHANNEL NUMBERS"? 



By RALPH H. LANQLEY 

Croslty Radio Corporation 



ONE of the most practical and interesting sug- 
gestions tending to simplification of radio 
as far as the non-technical user of radio re- 
ceivers is concerned is that of Mr. Langley, which 
be so interestingly discusses in this article. The 
use of radio receivers will become more and 
more widespread as the receiver becomes more 
simple to operate. Great strides in this direction 
have been made, what with single-control operation 
and direct light-socket powering of sets. But still, 
thousands of listeners who don't even know the 
difference between alternating and direct cur- 
rent, try to solve the dual mysteries of wavelengths 
and kilocycles which confront them in their local 
newspaper radio programs and on the dials of their 
receiving sets. Mr. Langley rightly asks, why should 
they bother with this wavelength-kilocycle terminol- 
ogy? Frequency calculations in kilocycles or 
meters if you belong to that school are important 
and necessary for the engineer and the technician, 
but the listener has no earthly concern for them. 

A committee of the National Electrical Manu- 
facturers' Association has been appointed to con- 
sider Mr. Langley' s suggestion and to take appro- 
priate action. That committee consists of R. H. 
Langley, chairman; L. W. Chubb, George Lewis, 
M. C. Rypinski, J. M. Skinner, R. H. Manson, 
and A. E. Waller. THE EDITOR. 



^ERHAPS there is no such thing as "the aver- 
age broadcast listener." But millions of them 
come pretty close to the average, and I wonder 
just what they think when they hear the announcer 
say that he is broadcasting "on a frequency of twelve 
hundred and sixty kilocycles." In all but a very few 
cases, I venture to say that their thoughts have 
nothing to do with the meaning of these words. Last 
year it was a "wavelength of two hundred and 
ninety one and one tenth meters" and that was even 
worse. Why so many numbers and so many strange 
words? 

Wavelength in meters, and frequency in kilocycles; 
related to each other by some mathematical law, and 
yet not related to anything the man in the street has 
ever heard of. Even the radio engineer must resort 
to a tabulation or a slide rule to translate one into 
the other, and yet each and every broadcast listener 
is expected to use them when he wants to hear his 
favorite stations. The newspapers print them, and 
you are expected to know, or somehow to find out, 
where they all come on the dials of your receiver. 

The change from "wavelength" to "frequency" 
was, of course, a very logical one. It can easily be 
demonstrated that the current in your receiver or 
in the distant transmitter has a frequency. The wave 
out in space is the thing that has a wavelength (as 
well as a frequency). Primarily we are not interested 
in the wavelength out in space but the currents in 
the receiver which the listener can hear. Then 
again, the wavelength listings were irregular and had 
to be given with at least four figures and a decimal 
point. The frequencies are given in three or four 
figures, and the last one is always a zero, because 
the frequencies are spaced in multiples of ten. But 
they start at 550 and stop at 1500, and the system 
is still far from being simple for Mr. Average 
understand. 

Some manufacturers have tried to put these strange numbers 
on the dial of the receiver when it was built. Then if you knew 
and could remember the wavelength or the frequency of the 




zoo 



Listener to 



station you wanted to get, you could 
set the receiver to that point, and there 
was the station. There were a lot of me- 
chanical difficulties in doing this, but 
more than anything else, it was the com- 
plexity of the numbers themselves that 
kept the conventional "zero to one hun- 
dred" dial on the sets. Here, of course, is 
another set of numbers, that must be read 
from a dial and related to the wavelength or 
the frequency or the call letters of the sta- 
tions. It is no secret that the average lis- 
tener does not know to whom he is listening, 
or how to find a particular station, except 
in the case of a very few that are near to 
him. The others are too hard to find, and 
many that he could hear and hear well, he 
does not bother with. 

It would be possible to record the loca- 
tions of our homes and places of business 
by their latitude and longitude. Your home 
address, for example might be given as 
"north 43 28' 37.42", east 76 18' 58. 1 3"." 
That would be just about as easy and just 
about as logical and just about as technic- 
ally correct as wavelength in meters or 
frequency in kilocycles for a broadcasting 
But our houses and our offices are con- 
veniently numbered and so are our telephones. Why 
not, then, use plain simple numbers for the broad- 
cast frequencies and wavelengths? 

"This is station XYZ on Channel 16." When you 
want station XYZ again, you will turn to the number 
1 6 on the dial. There will be numbers on the dial 
running from I to 96, representing the 96 broadcast 
channels. You will soon remember the fact that your 
favorite stations are at 16, 23, 38, 67, and 84. If 
you notice in the paper that station PQR, on channel 
53, is giving an unusually good program, there will 
be no difficulty about finding it. And the numbers 
will be the same on all receivers. When you trade in 
the old set, or when you go over to John's house, 
you will not be at a loss to know where to find the 
stations. 

A DIAL WITH NINETY-SIX NUMBERS 

IT WILL be more desirable, of course, to arrange 
a dial with these simple numbers, than it is to 
make one that reads in frequencies from 550 to 1 500, 
or in wavelengths from 199.9 to 545.1 with tenths 
on every one of the 96 of them. And there will not 
be any unnecessary "meters" or "kilocycles" tied 
to them. They will just be plain numbers like the 
one on your front door. You can have a table showing 
the wavelengths and frequencies corresponding to 
the channel numbers if you want it; the newspapers 
and the magazines will print them. But the average 
listener will not want any such list; he will have no 
use for it. 

Some day the range of frequencies allotted to 
broadcasting may be increased. When this is done, 
it is almost certain to be in the direction of the 
short waves. Then our series of 96 numbers will 
have to be continued, from 96 up. By starting the number series 
at the long-wave or low-frequency end, we shall leave room 
for expansion into the short waves, and we shall also have the 
smaller numbers for those channels now assigned to the larger 
and more widely known stations. 



1500 



L 



'ECEIVERS L $ 175 or less 

<J 
AVERAGE CITIZEN 




T IS an erroneous impression that to possess a modern radio receiver combining 
* both artistic merit and fidelity of reproduction one must spend an inordinate 
amount of money. The fact is that set makers have produced electrically good re- 
ceivers and housed them in cabinets that will grace any homeand all at a genuinely 
moderate price. This and the following pages show attractive moderate-priced re- 
ceivers ranging in cost from $175 to less than $100. The inspiration for the Bosch 76 
receiver shown above is Gothic and it is evident how effectively it may be combined 
with the furnishings of many a living room. This six-tube RFL circuit receiver uses 
either a loop or antenna and has an interesting volume control and vernier tuning 

adjustment. Its price is $175 



20 



NOVEMBER, 1927 



THE "MILAN" 

A cone loud speaker is supplied with 
this Apex receiver, the price for chassis, 
cabinet, and loud speaker, being only 
$135.00. The circuit comprises six 
tubes, the audio amplifier employing 
impedance coupling, which is respon- 
sible for excellent quality of reproduc- 
tion. The set is fully shielded and a 
single dial controls the tuning 



BELOW 

The Kennedy " Co- 
ronet." priced at 
$125.00. Seven 
tubes, including 
four matched r. f. 
stages, are used 



FOR LESS THAN $100 

The Workrite 17 has an all-metal chassis, 

shielded r. f. coils, single-control illuminated 

drum dial, and a combination switch and 

volume control. Price $95.00 



BY AUDIOLA, CHICAGO 
A six-tube console receiver for 
$110.00. There are three r. f. 
slates, and tuning is accom- 
plished by means of a single 
knob 




WHAT $70.00 WILL BUY 
A table model of the Fresh- 
man "Equaphase." As de- 
scribed elsewhere in this is- 
sue of RADIO BROADCAST, 
the "Equaphase" principle 
makes possible the elimi- 
nation of the cause of os- 
cillation 



THE "IROQUOIS" CON- 
SOLE 

This attractive six-tube, 
one-dial recei ver, by Mo- 
hawk of Chicago, retails for 
$130.00. less accessories, 
for battery operation. For 
electrical operation the re- 
ceiver may be obtained at 
an additional cost of 
$110.00, in which case it 
is complete with accessories 



AN EXAMPLE OF COMPACTNESS 
Here is a six-tube receiver by Stewart-Warner which 
is offered at $80.00. There are three r. f. stages, one 
of which is untuned. A single dial controls tuning, 
but there is an auxiliary one for bringing the an- 
tenna circuit into exact resonance, and also a vol- 
ume control 



NOVEMBER, 1927 



21 




OF THE NEUTRODYNE FAMILY 

For $100.00 it is now possible to obtain 
a single-control neutrodyne receiver. 
The Freed- Eisema tin 1SR-9 is such a 
receiver and, in addition to the single- 
control feature, it is completely shielded 
and has a pilot light on the front panel. 
Equal amplification throughout the 
broadcasting frequency spectrum is 
claimed by the manufacturers 



BELOW 

The "Warwick," at $138.00, is 
one of the offerings of Amrad 
for the 1927-28 season. It is a 
single-control neutrodyne, com- 
pletely shielded, and may be 
used with either loop or antenna 




BY SPLITDORF 

This is a receiver for the man who still 
believes in two-dial tuning. There are 
six tubes in all, three of these being 
r. f. stages. It is wired for use of a 
power tube in the last audio stage. The 
price is $75.00. The elliptical cone 
shown is priced at $35.00 



MCMILLAN'S "RIDGEWAY" 
Yet another shielded six-tube, 
single-control receiver, this one 
being priced at $110.00. A long air 
column and deep-toned horn are 
included. There is ample space for 
batteries or power equipment 




ZENITH MODEL 12 
Single control is again manifest in this 
six lube receiver, four variable con- 
densers bcinj,' manipulated by :i simple 
movement of the illuminated dial. The 
chassis is of metal, and the receiver is 
completely shielded. The cabinet is of 
mahogany. Price $100.00 



What Receiver Shall I Buy? 

r PHE moderate-priced receivers exhibited at radio 
-^ shows throughout the country this Fall are at- 
tracting widespread attention because the offerings in 
this class more than those in any other price range 
present greater values than ever before. Radio is now 
old enough so that those who bought radio sets two and 
three years ago are now thinking about replacing the 
old outfit with a more modern and satisfactory one. 
These pages show a few of these decidedly interesting 
receivers which can be had at a moderate price and 
which at the same time guarantee excellent electrical 
performance. These receivers are simple to control, more 
than ordinarily compact, and what is of growing im- 
portance, are handsome. There are table receivers for 
those who have but little space for a set, and more pre- 
tentious console sets for those who want both a radio 
receiver and an attractive piece of furniture. Practically 
all the console models in the medium-price range not 
only provide space for a loud speaker but also have 
convenient compartments for A and B socket power 
units and the convenient relay switch which, through 
the on-off switch on the receiver panel, controls both A 
and B units. Many buyers are interested in the console 
set with these compartments because they can at any 
time purchase A and B units for their set and, in effect, 
completely "socket-power" it. 



22 



LOUD SPEAKERS AND POWER EQUIPMENT 



NOVEMBER, 1927 



A ROLA CONE 

Here is a table model of the well-known 
Rola cone loud speaker, retailing at 
$28.50. This unit is equipped with a 
low-pass electrical filter lor the elimi- 
nation of tub?, distortion. The heavy 
turned-wood disk serves as an acous- 
tical battle surface. 



FOR A AND B CURRENT 

This Philco power unit will pro- 
vide 180 volts at 60 mils., and there- 
fore is adequate for a receiver em- 
ploying six or more tubes, with a 
power tube in the output stage. 
The unit, costing $79.50, is sup- 
plied in an attractive metal rase. 
A built-in trickle charter keeps the 
A battery in good condition 




A CONSOLE LOUD 
SPEAKER 

The exponential horn type 
of loud speaker, of which 
this is an example, is be- 
coming increasingly popu- 
lar, due to its excellent 
reprodm ing qualities. The 
one here is by Temple, 
Chicago, anil lists at $65.00 



THE "UNIPOWER 

A trickle charger and storage 
battery are. combined in this 
useful device by Gould. It 
may be obtained in either a 
four- or six-volt output form 





AN 



INEXPENSIVE 
CHARGER 



A six-volt storage battery may 
be quickly charged with this 
device, a product of the Valley 
Electric Company. St. Louis. 
The charging rat* is 6 ami>eres 
and the price, $19.50 



FOR A AND B CURRENT 

Another device which is capable of 
run vert ing your a. c. house current 
into suitable power for your receiver 
by Kxide. The B output is 180 volts 
maximum, while the A supply is six 
volts. A trickle charger keeps (he A 
battery well charged. The approximate 
cost of operating this device is one cent 
an hour 




AN EXPERIMENTAL SET-UP 

This photograph, taken about four years ago in RADIO BROADCAST Laboratory, shows some 
of the early photograph transmission and reception apparatus designed by the author 



RADIO BROADCAST Photograph 



How the Cooley a Rayfoto 




THE articles announcing a system of radio 
picture reception appearing in the Septem- 
ber and October issues of RADIO BROAD- 
CAST have attracted widespread attention among 
radio experimenters. Even without specific data 
as to the actual operation of the Cooley " Ray- 
foto" system, experimenters have been fairly 
besieging the writer since the appearance of these 
articles and the demonstration of the " Rayfoto" 
transmitter and receiver at the New York Radio 
Show. 

All the obstacles to making this new field 
available to the experimenter are being removed, 
one by one. Engineers are busy designing com- 
ponents and manufacturers are busy getting into 
production to meet the demand. And, for the 
broadcasters, an important method of supplying 
broadcasting stations with "picture" programs 
has been evolved. In this article we shall sketch 
briefly just how the Cooley "Rayfoto" system 
functions, what each part does, and what its 
purpose is. These technical details will give the ex- 
perimenter a clear picture of what the difficulties 
are and what technical knowledge is needed for 
him to assemble and operate the apparatus. The 
Cooley "Rayfoto" recorder is no more difficult 
to build than a five-tube receiver. 

THE SYSTEM IN BRIEF 

IN A few words, the cycle of transmitting and 
receiving a "Rayfoto" picture is as follows: 
The subject, any ordinary positive or negative 
print, is placed on the drum of the transmitter 
or converter which revolves and feeds it along a 



By AUSTIN G. COOLEY 

shaft before an optical system, which, in turn, fo- 
cuses the reflected light on to a photo-electric cell. 
The amplified currents from this cell are 
8oo-cycle audio-frequency currents varying in 
amplitude in accordance with the subject. 
These currents control the radio transmitter 
output and the signals are received on a con- 
ventional broadcast receiver. They are then fed 
into the "Rayfoto" printer which produces a 
corona discharge in accordance with the strength 
of the received signal. The corona discharge 



All you need for picture reception is a 
standard receiver, an oscillator, a 
stop-start motor mechanism, photographic 
paper, and enthusiasm. The important 
part of the receiving mechanism is the 
motor mechanism. Wiib oscillators and 
receivers we are all familiar. The motor 
mechanism and all other necessary 
components duly approved and labelled 
with the Cooley Rayfoto label will soon 
be on the market. Those eager to be the 
first in their communities to receive pic- 
tures by radio may send their names and 
addresses to RADIO BROADCAST and 
these will be sent to the manufacturers 
making the parts. The total cost will 
not be more than $100. THE EDITOR 



takes place at the point of a corona needle which 
feeds along a revolving drum as the needle traces 
over a photographic paper wrapped around the 
drum. At the end of each revolution of the drum 
the received signals are diverted from the 
printer unit to a relay which is actuated when a 
synchronizing signal is received at the beginning 
of the revolution of the convertor drum. This 
relay in turn operates the trip magnet which re- 
leases the recorder drum so it may start off at the 
same time as the convertor drum. After the 
needle has fed along the entire length of the 
paper, the latter is removed from the drum, 
developed, washed, fixed, and washed again. 
The result is a picture of a prize fighter who has 
been knocked out a few minutes before; or a 
picture of a railroad wreck just occurred; or 
maybe a picture of some sweet young thing 
who may have won a bathing beauty contest in 
the afternoon. 

Phototelegraphy is not complicated and in- 
volves nothing that is really new in physical 
science, but many of the "kinks" involved must 
be well understood if good initial success is to be 
expected. Most of the difficulties ordinarily in- 
volved in picture reception work will be pre- 
vented because manufacturers will supply equip- 
ment especially designed for the purpose and 
if the experimenter understands the principles 
of the system and can handle amplifier and oscil- 
lator circuits, he should have no difficulty in 
setting up his "Rayfoto" recorder and having 
good picture reception right from the beginning. 

All systems of phototelegraphy have one 



24 



RADIO BROADCAST 



NOVEMBER, 1927 



limitation in common: They can transmit only 
one shade and one unit area of the picture at a 
given instant and therefore transmission must be 
accomplished by dividing up the subject to be 
transmitted into thousands of small areas. 

The " Rayfoto" and many other systems trans- 
mit the signals for each unit area in rapid suc- 
cession and the resultant signal varies in ampli- 
tude in accordance with the shading of the pic- 
ture. The speed at which the impulses are trans- 
mitted depends largely upon the ability of the 
receiving apparatus to reproduce rapidly the 
electrical impulses on the recording medium. 
The corona method of printing used by the 
Cooley "Rayfoto" system is capable of printing 
faster than any other system the author knows 
of, but for simplicity and low first cost we are 
using a signal frequency of about 800 cycles per 
second, which does not permit printing as rapidly 
as is possible with the system when higher fre- 
quencies are used. The possibility of operation at 
higher frequencies has been taken into consider- 
ation in designing the present equipment so that 
the speed of transmission can gradually be in- 
creased without necessitating any radical changes 
in equipment. 

As explained in the October issue of RADIO 
BROADCAST, the picture or subject to be trans- 
mitted is placed, at the transmitting station, 
upon the drum of the picture transmitter, which 
we will hereafter call the "convenor." A small 
spot of the picture is illuminated and the re- 
flected light from this spot actuates a photo- 
electric cell, the signals from which control the 
radio transmitter after the photo-electric cell 
currents have been sufficiently amplified. Each 
time the drum is revolved, the spot of light 
traverses a different path an eightieth of an inch 
wide across the picture. The line is broken up 
into 480 sections by the optical system so that 
480 electrical impulses are transmitted every 
revolution of the drum and each impulse cor- 
responds in intensity to the reflected light from 
a small area of the picture. The result is that 
480 electrical impulses are transmitted for each 



revolution of the drum, or about 800 per second 
when the drum is making one hundred revolu- 
tions per minute. Running at this speed the drum 
feeds along the shaft 1, Fig. i, at the rate of 
one and a quarter inches per minute. The drum 
is two inches in diameter and about five inches 
long. This will give us an operating speed of four 
minutes for a five-by-six-inch picture. 

The beginning of each revolution is marked 
by an impulse made up of twenty strong 800- 
cycle signals in succession. This impulse is used 
at the receiver to start the recording drum off at 
exactly the same time as the transmitter drum, 
for it is necessary that the two drums start off 
together. To accomplish synchronism in this 
way, known as the "stop-start" method, the 
recording drum must start a revolution at the 
same instant as the transmitter drum. It is neces- 
sary that the recorder drum run slightly faster 
than the converter drum, then stop at the end 
of the revolution for an instant until the con- 
verter drum completes its revolution. A trip 
magnet operated by the strong synchronizing 
impulse releases the recording drum at the 
proper time. 

This trip magnet is operated through a relay 
which is connected to the rest of the system only 
after the revolution of the recording drum has 
been completed. Between the time the recorder 
drum stops and the time the synchronizing im- 
pulse is received, there must be no strong signals 
received, so we paste a strip of white paper at 
the end of the picture being transmitted so the 
signals will be weak while the recorder drum is 
stopped. Should a crash of static or some other 
disturbance be received during this waiting 
period, or "recorder lap," as it is called, the re- 
corder drum will be released in advance of the 
synchronizing signal. By making the recorder 
lap very small, the danger of such a " static slip " 
will be reduced proportionately. The wider the 
white strip on the picture being transmitted, the 
greater will be the chances of a good start after 
a static slip so that the only marring effect will 
be one line slightly out of place. 




RADIO BROADCAST Photograph 
SOME EARLY "RAYFOTO" EQUIPMENT IN RADIO BROADCAST LABORATORY 

The apparatus on the right of this picture is a Cooley photograph transmitter and in the center is an 

amplifier and "corona" apparatus. The picture receiver at the left has been redesigned in many ways 

to make its operation as simple as possible. This apparatus was photographed four years ago 



We will consider here a few of the principles 
involved that affect the characteristics of the 
received picture. In picture work, we wish to 
reproduce at the recorder shades of light and 
dark corresponding exactly to those of the 
transmitted subject. The light reflected from the 
subject varies the current through the photo- 
electric cell in a ratio almost directly with the 
intensity of the light, and this current, after 
amplification, is made to control the power input 
to the radio transmitter modulator which there- 
fore varies directly proportionately to the re- 
flected light, due to the characteristics of the 
Heising modulator. 

The final modulated radio signal sent out 
over the air will vary as the square root of 
the reflected light. The received signal is am- 
plified lineally in the radio-frequency stages 
of the receiver. The detector output varies as the 
input squared, however, and therefore the cur- 
rent in the plate circuit of the detector will be 
directly proportional to the reflected light. The 
signal then can be amplified in the audio ampli- 
fier and delivered to the " Rayfoto" printer with 
an intensity directly proportional to the reflected 
light at the transmitter. 

Limited by the data available at the present 
time, this is as far as we can go with the signal 
and know definitely what we are doing in the 
way of maintaining the proper signal ratio 
through the various circuits. We have no exact 
data on the relation of the input to output of the 
Cooley " Rayfoto" printer. Also we do not know 
the relation of the power delivered by the 
" Rayfoto" printer to the effect it has on the re- 
ceiving paper. This factor is quite flexible and 
can be controlled considerably by the selection 
of the printing paper and its time of develop- 
ment in the photographic solutions. The printing 
paper we recommend today probably will not 
be the paper you will be using next year. It is 
therefore necessary to have some control over 
the system so we may match our amplification 
characteristics to conform with those of the re- 
cording paper we may choose to use. For ex- 
ample, if the received picture does not show 
sufficient contrast in the lighter shades but too 
much in the darker shades, we must adjust our 
amplification characteristics to correct for this. 
One way it can be done is to reduce the filament 
voltage on one of the amplifier tubes so that the 
strong signals are cut off somewhat by running 
over the top knee of the characteristic curve 
while the signals of lower value are on the straight 
portion of the curve. Additional correction may 
be obtained by reducing the time of development 
in the photographic solution. 

The most convenient place for signal charac- 
teristic control is in the detector circuit, because 
of its "squared" characteristic. This character- 
istic may be varied considerably by proper pro- 
portioning of the grid condenser and grid leak. 
If the grid leak can be brought down to a very 
low resistance, say 500 ohms, and the plate 
voltage made adjustable over a range of from 4 
to 40 volts, additional control of considerable 
value will be gained. Instead of varying the plate 
voltage, a variable grid battery may be used. 

EFFICIENT AUDIO STAGES NECESSARY 

A GOOD picture must not only represent exact 
shadings of the subject but it must also 
show up most of the small details of the original. 
A poor audio amplifier system will blur up the 
details in black shades and will not permit any 
of the details in the light shades to appear. The 
amplifier must not oscillate at any audio or 
super-audio frequency or even tend to oscillate. 
Oscillations in audio amplifiers most generally 
occur because of feed-back through the B bat- 
teries from one stage to another and can be pre- 



NOVEMBER, 1927 



HOW THE COOLEY "RAYFOTO" SYSTEM WORKS 



25 



vented by the use of low-resistance batteries, a 
very large condenser across batteries of moder- 
ately high resistance, or by the use of inde- 
pendent batteries for the audio amplifier. The 
first pictures transmitted will contain sufficient 
contrast so that imperfect amplifying charac- 
teristics will not appear very noticeable. Never- 
theless, the progressive experimenter should try 
to keep one step ahead of the game. 

The plate current drain on the B batteries due 
to the Cooley "Rayfoto" printer will be about 
10 or 15 milliamperes, so that the total current 
drain of the printer and an ordinary five-tube 
receiver will be in the neighborhood of 45 mil- 
liamperes. However, this additional drain of 
15 milliamperes will only be present when the 
printer is being used and, since it will not be 
operated for long periods at a time, an ordi- 
nary set of B batteries should be good for 
many months of service. A total voltage of 
about 200 volts is required. 

Naturally an amplifier that can be operated 
without oscillating is much more efficient than 
one that tends to oscillate and which therefore 
requires the introduction of some loss to prevent 
oscillations. In many cases, however, it is more 
convenient to use an amplifier we already have 
and which can be "doctored" up a little to make 
it serviceable for " Rayfoto" work. A resistance 
across the secondary of one or more of the trans- 
formers will prevent the amplifier from oscillat- 
ing. The required resistance may vary between 
100,000 ohms and 2 megohms. 

Many broadcast receivers have sufficient am- 
plification in their own system so that additional 
audio amplification is not necessary. You may 
test out your receiver in the following manner 
to determine whether any additional amplifica- 
tion is required to operate the recorder: Place a 
milliammeter in the plate circuit of the last 
amplifier stage; cut the current down to 0.2 
milliamperes by increasing the C battery poten- 
tial; short-circuit the loud speaker terminals; 
then tune-in a local broadcasting station. If the 
milliammeter jumps up over 15 milliamperes, no 
additional amplifier stage is needed. Even if it 
only goes to ten mils, it will not be necessary to 
use the added stage but this amount of current 
will allow only a very small margin of safety. 



If an added stage of amplification is required, a 
special transformer should be used, one that is 
capable of operating without saturation and 
which will not produce oscillations in the audio 
system. Special transformers for this work will 
soon be available. 

The Cooley "Rayfoto" printer is the device 
for producing the corona discharge that affects 
the photographic recording paper. It converts 
the received audio-signal into a fluctuating source 
of light corresponding to the transmitted signal. 
This unit consists of a modulated oscillator feed- 
ing a corona coil. The corona discharges are 
secured from the high-voltage side of the corona 
coil secondary winding. 

Readers may wish to have some explanation 
of the nature of the corona we refer to here. 
Visually, the corona discharge at the needle point 
riding on the paper is a small spray of blue sparks 
similar in appearance to those produced by a 
violet-ray machine. This discharge occurs when 
a difference of potential of 13,000 to 26,000 volts 
per centimeter (which, incidentally, won't hurt 
you) exist around the needle point. This potential 
is produced by the radio-frequency amplifying 
transformer, known as the corona coil. The pri- 
mary of this coil is part of a vacuum-tube oscilla- 
tor operating at a frequency of 333 kc. (about 900 
meters). The plate circuit is supplied by the sig- 
nals from the radio receiver. After being amplified 
to supply enough power to the modulation trans- 
former, these signals are strong enough to produce 
a strong corona discharge when strong signals are 
received. For the sake of efficiency and shading, 
about one hundred volts of direct current is sup- 
plied, in series with the modulation transformer 
to the plate of the oscillator. This boosting 
voltage must not be sufficient to produce a corona 
that will print when weak signals are coming 
through. 

The oscillator of the "Rayfoto" printer radi- 
ates for some distance if the frequency is high, 
and to prevent such interference we have chosen 
the reasonably low frequency of about 333 kc. 



We do not recommend an oscillator frequency 
corresponding to more than this unless careful 
shielding is used. 

The "Rayfoto" recorder is the mechanical 
unit of the system which consists of the re- 
ceiving drum driven by a motor and controlled 
with a "stop-start" system of synchronizing. 
A screw feed arrangement feeds the corona needle 
along the drum as it revolves so that the needle 
moves along at approximately the same speed 
that the converter drum as the transmitter 
moves along its shaft. 

The "stop-start" mechanism consists of a 
slip clutch between the motor drive and the 
drum, and a trip magnet arrangement that stops 
the drum at the end of each revolution until the 
synchroi. izing impulse is received. This impulse 
trips the armature of the magnet which operates 
through a relay. By this system, the transmitter 
and receiver are synchronized about twice a 
second, thereby eliminating much delicate and 
expensive synchronizing apparatus. 

The recorder drum is the same size as the one 
at the transmitter but since the recorder has a 
slight "lead," that is, runs slightly faster than 
the converter drum, the received picture will 
be stretched out a small amount, depending 
upon the amount of lead. To compensate this, 
the gears between the drum and screw feed 
shaft will be of such a ratio that the needle will 
feed along a little faster than the transmitter 
drum so that the proper proportions are restored. 
As a result the received picture will be slightly 
larger than the one transmitted. 

It is desired to keep the lead as small as possi- 
ble so as to prevent excessive stretching of the 
picture. Also, if the lead is too much, the trip 
magnet may be tripped from a subject signal 
instead of the synchronizing signal. If the lead is 
too small, the synchronizing signal may be re- 
ceived before the recorder drum has finished 
its revolution and has switched the relay in the 
circuit. Consequently the relay will be operated 
by the next strong subject signal. 



Complete constructional data for a Cooley 
Spot Of lighten picture " Ra y foto " receiver which may easily be made 
at home is scheduled for next month's RADIO 
BROADCAST. 



Lens to focus _- 

lighten picture 

Glass prism to change 
direction of light _ 

Photo-electric cell - 



Output signals from cell consist of audio- 
freqency currents of varying amplitude. 

Frequency is determined by speed of disk," 
and amplitude by shading of picture 



To amplifier and radio transmitter 

Light is broken up by passing through 
holes in revolving disk. Frequency 
determined by speed of disk 




Picture being transmitted 



"Converter" drum moves^downward 

along threaded shaft y 8 o every revolution 



-- Holes in disk interrupt 
light from lamp L 



Motor drives disk and drum 



A PICTURE DIAGRAM OF THE COOLEY TRANSMITTER 

This drawing shows graphically how the Cooley picture transmitter produces electrical sig- 
nals varying in strength in accordance with the shading of the picture being transmitted 



IN Stromberg- Carlson 
receivers, a manufactur- 
ing refinement, not evi- 
dent to the casual ob- 




server, is found in the 
cord connecting the set 
to the light socket. It is 
made with unusual care 



THE MODERN RADIO RECEIVER 

By EDQAR H. FELIX 



THE modern manufactured receiver has 
become a precision product, built under 
most exacting conditions prescribed by 
skilled engineering departments. It is no longer 
a heterogeneous combination of parts, wired to- 
gether in conformation to circuits supposedly 
possessed of magical qualities. Performance is 
the product of a thousand and one engineering 
decisions carried out with a care so far above and 
beyond that which the average buyer can ap- 
preciate that engineering refinements are no 
longer considered suitable as selling arguments 
by which to sway the buyer's preferences. 

Where should the by-pass condenser across 
the filament leads be placed? Is the improved 
performance attained by placing it directly 
underneath the tube sockets sufficient to warrant 
a special moulding? Does a one per cent, differ- 
ence in moisture content of the insulating paper 
of fixed condensers reduce losses sufficiently to 
justify an additional cost of twelve cents per 
receiver and does that involve an increasing 
percentage of condenser breakdowns? Should 
three more turns be used on the radio-frequency 
transformer primary to get slightly improved 
quality or does that involve a sacrifice in selec- 
tivity too great to be permitted under present 
broadcasting conditions? Should the audio-fre- 
quency system be designed to cut off at 5500 
cycles or at 4800, in the first case giving slightly 
improved reproduction; in the other, slightly 
reducing the effect of certain types of interference 
noises? 

It is such highly technical questions as these, 
clouded in a veil of mystery to all but the ex- 
perienced radio engineer, that makes one radio 
set better than another. The placing of a socket 
half an inch one way or another may make an 



imperceptible difference in performance, but it is 
the multiplication of such details, carefully de- 
termined after engineering study, that assures 
the buyer of his money's worth. 

In a sense, we have come to a parting of the 
ways between the factors that make real radio 
performance and those which make up the buy- 
er's mind between one radio set and another. 
There is a premium on the little, superficial 
improvements which the buyer can appreciate 
because they are the only practical ways of ex- 
pressing engineering ingenuity to the ultimate 
consumer. 

ONE REFINEMF.NT OF FADA 

'"THE Fada receivers of this year, for example, 
1 employ a new simplified power switch and 
volume control, an obvious convenience which 
any prospective purchaser will appreciate. One 
control takes the place of two. Hidden in 
the beautiful cabinet, is a chassis made of A 
inch pressed automobile body steel. It is sup- 
ported on a three-point suspension with absolute 
rigidity so that the parts mounted in it cannot 
get out of alignment. The accurate matching of 
variable condensers contributes not only to se- 
lectivity but to quality of reproduction. In past 
years, an accuracy of one per cent, in capacity 
throughout the tuning range has been considered 
satisfactory. The Fada condensers are matched 
to an accuracy of j of i per cent, and the same 
standard is applied to the tuning inductances 
coupled with them. These are a few of the hidden 
values which make for good performance. 

The shaft on which the tuning drums and var- 
iable condensers are mounted is one-half-inch 
flash copper plated piston rod steel and is gauged 
to a tolerance of .0005 of an inch! The day of the 



curtain rod condenser support is over. The pis- 
tons in your automobile are gauged to no closer 
tolerance. 

Advertisements shout uniformly about the 
most selective receiver with the best tone quality, 
but give the discriminating buyer no real facts 
to help him appreciate the performance of a 
receiver. Generalities may sell the uninformed 
and help to create name familiarity, but sterling 
worth, built in by ingenious engineering and 
painstaking manufacture, is hardly ever con- 
veyed to the reader of advertising. 

GOOD THINGS YOU DON'T SEE 

ANOTHER instance of superficial selling 
points which make an obvious appeal to 
the uninformed buyer and the equally important 
hidden refinements which contribute even more 
significantly to good performance is found in 
the Freed-Eisemann receiver. Several models are 
equipped with a voltmeter so that the set owner 
can readily check the A, B, and C voltage applied 
to every tube of his receiver. Since accurate 
voltage supply is of vital importance in the per- 
formance of the receiver, the selling value of that 
feature is obvious. But how many buyers know 
of the two special bonding clips which ground 
the shielding of the detector stage in order to 
dissipate more readily the radio-frequency cur- 
rents generated in that shield? It is a minor point, 
but an expression of the engineering care which 
makes the modern radio receiver. 

Recently, the writer visited the Stromberg- 
Carlson factory at Rochester, New York. A com- 
plete understanding of the refinement which is 
concealed in the cabinet of the Stromberg-Carl- 
son receiver hardly ever penetrates beyond the 
monument to engineering skill and idealistic 



NOVEMBER, 1927 REFINEMENTS OF THE MODERN RADIO RECEIVER 



27 



production standards which that new factory 
actually is. One could write a thousand words on 
how the cord by which you tap the a. c. power 
line is made! Only a detail, but it assures unfail- 
ing service for a period of years. It means no 
frayed cord and no breakdowns, an advantage 
which passes practically unnoticed in the atten- 
tion of almost every buyer of that receiver. But 
to give him that advantage, special engineering 
standards have been set for every item of ma- 
terial used in the flexible cord. The fine copper 
wires which, woven together, make an everlasting 
cable, are ten times as strong as ordinary wire. 
Special flexible conductor, which does not break 
if sharply bent, is employed. The individual 
strands are so fine that they cut the finger like 
a razor blade. Covering these wires are insulating 
materials adding a factor of safety far above 
and beyond that considered necessary. And 
finally, selected cotton is woven over the insulat- 
ing material, giving a mechanical strength so 
that the copper wire itself is relieved of most of 
its load. Last, but not least, comes an outer cov- 
ering of silk so woven that there will be no un- 
twisting of the cable and it will hold its lustre 
for a period of years. Outwardly, there is but 
little to distinguish this little engineering master- 
piece from an ordinary power con- 
necting cord which will fray, untwist, 
and break in the course of time, par- 
ticularly if it must be pulled out each 
time the vacuum cleaner is used. 
Probably not one salesman in ten 
thousand selling the Stromberg- 
Carlson receiver ever considers this 
refinement one of a thousand which 
conscientious engineering has built 
into that product. 

SOMETHING ABOUT CONDENSERS 

ONE feature which every radio 
enthusiast appreciates is the 
advantage of straight frequency-line 
tuning condensers over the straight 
capacity-line type. The desirability 
of even spacing of stations over 
the tuning dial throughout the 
broadcast range is obvious. But, 
with the almost universal tendency 
toward multiple condensers, needed 
to obtain single control, the neces- 
sity for straight frequency-line condensers has 
caused many an engineer gray hairs. It is very 
difficult to secure uniformity in quantity 
with condensers having the peculiarly shaped 
plates necessary in straight frequency-line tuning. 
With straight capacity-line used in connection 
with matched inductances, uniformity is easily 
attained and tuning circuits readily matched. 
All that need be done to match the stages is to 
adjust the condensers at any point on the wave- 
length scale, after the receiver is assembled. 
Once that is done, absolute accuracy is likely to 
obtain at all dial settings. But straight capacity- 
line condensers mean that, at the short wave- 
length end of the dial, stations are hopelessly 
crowded, while, at the upper end, they are widely 
and wastefully separated. 

A fine example of engineering refinement in 
meeting this problem is embodied in the Federal 
receiver. Condensers with square plates, sliding 
in rigid grooves, assure absolute uniformity of 
capacity variations and attain a standard of 
accuracy almost impossible to secure with con- 
densers having specially formed plates to secure 
the straight frequency-line effect. But the buyer 
of a Federal does not sacrifice the advantages of 
straight frequency-line tuning by the use of these 
condensers. An ingenious and well designed gang 
tuning control mechanism gives him all the 
advantages of straight frequency-line tuning 



The mechanism is a masterpiece of mechanical 
design. 

Another example of true engineering beauty 
is embodied in the antenna tuning compensator 
which is a part of the mechanism. With multiple 
tuned circuits, the designer has the choice of 
several ways to compensate any variations in 
antenna capacity. He may use a broadly tuned 
antenna or input stage which gives but little or 
no amplification. Such a stage contributes its 
share of tube noise and accentuates nearby sta- 
tion interference. Or else he may employ a 
sharply tuned stage which has a separately 
adjusted compensating condenser. Of course, 
the most efficient and satisfactory method to the 
user is an antenna stage which tunes sharply and 
contributes its share of amplification. Those 
having receivers with a vernier antenna com- 
pensating condenser have noticed that, although 
they have a main tuning dial which gives the set 
the appearance of one control, they must actually 
adjust two dials the main tuning control and 
the compensator to tune-in a station properly. 

With the Federal receiver, the compensator is 
geared with the main tuning adjustment and 
automatically keeps the antenna circuit in step 
with all the rest throughout the tuning range. 




THE R.F. OSCILLATOR USED BY BOSCH TO MATCH COILS 



The author would not be surprised to discover 
that the electrical law determining the correct 
compensating adjustment needed for all types 
of antenna systems and working out the mechan- 
ical arrangement which assures adherence to 
that law was a bigger engineering job than 
designing the entire radio set marketed in 1924. 
All this engineering precision applied in design 
may be nullified by carelessness in production. 
The electrical and mechanical measurements 
made in the modern radio plant are of an order 
of precision unrivaled in any field of quantity 
production. Atwater Kent, for example, makes 
1 59 precise tests, each requiring engineering 
knowledge to perform, in producing a single 
receiver. Some of these tests entail mechanical 
precision measurements; others electrical meas- 
urement of currents of mere millionths of an 
ampere. But every test contributes to the pur- 
chaser's assurance of reliable radio service. 

MATCHING INDUCTANCES IN QUANTITY 

HOW one manufacturer applies engineering 
precision to production is best expressed in 
the words of William F. Cotter, radio engineer 
for the American Bosch Magneto Corporation: 
"The subject of sorting and matching of in- 
ductance coils is one to which we have given 
considerable thought. Its importance is recog- 
nized by every manufacturer. With one test 



fixture capable of handling the job, it would be 
comparatively easy to install a check of the 
manufactured product and be assured of a high 
degree of accuracy. However, when two or more 
test fixtures are required to handle the volume 
of coils manufactured, and where it is desired to 
check these coils at radio frequency, a more 
serious problem presents itself. 

" We have employed several methods over the 
last three years The one I describe, however, 
represents our latest development and is the re- 
sult of all our past experience. 

"A radio-frequency oscillator is built up 
around the standard 2O1-A tube. Incorporated 
in the tuned circuit of the oscillator at nearly 
ground potential is a resistance of approximately 
10 ohms. Across this resistance is shunted in 
series the coil to be tested and a variable con- 
denser with its separate vernier condenser. 
When this series circuit is brought to resonance, 
the total resistance of the shunt circuit comes 
down somewhat in the neighborhood of the 
lo-ohm resistance, and one-half of the oscillation 
current is diverted to the series tuned circuit. 
Included in this tuned circuit is, of course, the 
usual thermo-galvanometer. 

" By means of a properly chosen vernier con- 
denser, the coils coming through can 
be checked for accuracy and sorted 
in as many divisions as experience 
shows necessary. However, while 
this is suitable for one test fixture, 
the problem of keeping two or three 
fixtures oscillating at the same fre- 
quency presented itself. Naturally, 
if the frequency of the individual 
oscillators varies, say 10 per cent , 
it is quite impossible to group 
coils together just by dial readings. 
"We have solved this problem by 
building a crystal oscillator as one 
of the test fixtures. Other oscillators 
of ordinary type are built and each 
is equipped with a vacuum-tube de- 
tector. The oscillators are placed so 
that it is possible to couple in some 
of the energy from the crystal oscil- 
lator. By means of a headset, the 
operator adjusts his oscillator to zero 
beat with the crystal oscillator. Usu- 
ally, it is not necessary to check 
this setting more than two or three times a day. 
By this method, coils may be checked and sorted 
with an accuracy of a few tenths of one per cent." 
That is engineering refinement. It is the 
kind of "detail" which makes the 1927 radio 
receiver a precision product. 

The broadest appeal to the radio buyer, and 
one to which most people respond, by and large, 
is the outward beauty of the product and the 
name reputation of the manufacturer. Faced, as 
a prospective buyer is, with numerous products 
attractive from these standpoints, he is easily 
swayed from one brand to another by superficial 
selling points. The more discriminating and in- 
telligent buyer and in the radio field, because 
of the host of persons who have a smattering of 
technical knowledge, this class is predominant 
and influential looks to the hidden qualities, 
the expression of engineering ingenuity and 
manufacturing skill, as well as the performance 
qualities, in deciding between one receiver and 
another. The glittering generalities which have 
characterized successful advertising and have 
successfully built up huge quantity production, 
are at last beginning to suffer a reaction. There 
are too many "best" automobiles and too many 
"finest" radio sets. But facts, the refinements, 
the details, presented to those who can under- 
stand them, are indisputable evidence of inherent 
quality. 



A RADIO receiver, as any engineer will 
tell you, is a complicated and highly 
organized machine, designed to perform 
several functions none of which is independent 
of the others. It is because of these intercon- 
nected functions that the engineer will wish he 
were in Europe if you ask him: 

"What is the best radio?" 

An automobile, on the contrary, is compara- 
tively simple. It has but one function to perform, 
it must take energy in some inert form, say un- 
confined gasoline, and convert it into some other 
dynamic form which is useful in carrying some- 
one somewhere. 

To answer a question regarding the best auto- 
mobile, then, is simpler, especially since the auto- 
mobile industry has been established long enough 
for the most expensive car to be usually the best. 
Unfortunately, radio has not even this truth to 
go on, for, all things considered, the most expen- 
sive radio does not always pan out to be the best. 

A radio must do three things, and therefore 
there are three problems of design. They deal 
with: 

1. SENSITIVITY. The receiver must be sen- 
sitive enough to pick up the signals one wants 
and amplify them sufficiently to give good 
loud speaker volume. 

2. SELECTIVITY. The receiver must accept 
signals from the one station the owner wants 
and reject all others. 

3. FIDELITY. The loud speaker signals must 
be a faithful reproduction of the original in 
tone and in relative volume. 

Thus a perfectly selective and sensitive re- 
ceiver would pick up any station operating at 
any distance on any frequency, and would turn 
a deaf ear to all others, no matter how near the 
given station in frequency or distance, or how 
great their power. If the receiver has 100 per 
cent, fidelity of reproduction, signals as loud as 
the original would come from the loud speaker, 
and with all tones exactly as they originate in 
the studio. 

Needless to state, there is no such receiver. 

There are several reasons for this. As men- 
tioned above, these varied functions of a receiver 
depend upon each other, and not always to the 
same degree. For example, an infinitely selective 
receiver would be in the present state of the art, 
highly unsatisfactory from the standpoint of 
fidelity. Advertising writers to the contrary, one 
cannot have something for nothing, even in radio. 

There are those, however, who desire to know 
which of two receivers is the better, and among 
these are the reputable manufacturers them- 
selves. It is for this reason that set testing meth- 
ods have changed. 

Not so long ago, when a receiver had been put 
together and wired someone took it to a test 
bench where it was hooked to batteries and an 
antenna. If signals came out of a horn somewhere 
the set worked. It was sent to the dealer at once. 
This was an obvious test. 

The obvious, as we all know, is not always the 
best. In the case of good radio receivers, this 
older, obvious test has given way to more scien- 
tific tests which do not depend upon a smoke 
covered antenna or the often tired ears of a 
test man, but upon tireless and unemotional in- 
struments. 

In spite of the fact that these tests have been 
practised sporadically, we suspect in the bet- 
ter known laboratories, it has been only within 
the last half year that descriptions of them began 
to appear in the technical literature. So new is the 
industry that standard tests have not been de- 
veloped, nor have engineers even agreed among 
themselves regarding even the nature of these 
tests. Probably while this is being read, com- 
mittees of the various radio organizations and 




By KEITH HENNEY 

Director of the Laboratory 



radio engineering societies will be weighing con- 
ditions of test and endeavoring to set definitions 
of the perfect receiver, definitions that everyone 
will recognize. 

WHAT HAPPENS INSIDE THE BOX? 

NOW, before trying to find how much of any- 
thing a receiver does, it is well to get an idea 
of what happens inside the box, to discover if 
possible what should happen and how much. 
Then we shall have some idea of what to look for 
and what the relative order of magnitude will be. 
For example, harking back to the automobile, 
almost everyone knows that an automobile has a 
carburetor. Some people know what it is for; the 
writer does not. There is also a clutch and some 
other apparatus which everyone who is about 
to buy or run or design or fix a car should 
know all about. He should know what these 
various pieces of equipment are for, what hap- 
pens if you leave some of them at home, and 
when the car runs properly, what the magnitudes 
of the various operations are. The quantity of 
gas and oil per mile, or hour, revolutions per 
minute, miles per hour, ability to climb hills, 
"pick-up," etc., are all terms that have both 
definition and dimensions. 

A radio receiver also has several pieces of com- 
ponent apparatus. Each has a different function, 
and in each piece of apparatus something 
happens when the set is operating properly. 
What we must know first is what is each part for, 
how it does its work, and then how much should 
a good unit do? This will enable us to define a 
perfect receiver, and if we have laboratory equip- 
ment and patience, or if the manufacturers will 
supply us with the proper data, we shall be able 
to decide just where in the scale of goodness our 
particular receiver stands. 

The inner works of the receiver, except super- 
heterodynes, consist of three parts: a set of tubes 
which serve as radio-frequency amplifiers, boost- 
ing in magnitude the incoming signals without 
change in form and very sharply tuned; a de- 



tector more broadly tuned which changes the 
signals into an audible form; and third, audio 
amplifiers which bring the detector signals to 
loud speaker volume. The last are not tuned at 
all, or at least very broadly. 

The radio frequency amplifiers are intimately 
connected with the transmitting station. The 
receiving antenna or loop is situated in a reser- 
voir of energy, part made by man, part by nature; 
part useful, part disturbing. A fair share of this 
energy is created by broadcasting stations which 
pour their output into what scientists call the 
"ether" and what the layman calls the "air." 

The energy one wishes to receive speeds from 
the broadcasting station with the velocity of 
light, so fast that it may be heard from the loud 
speaker before it is heard in the rear of an audi- 
torium in which the broadcasting may occur. 
This is because sound travels through air at 
I loo feet a second and radio waves through the 
ether at 186,000 miles a second. 

The receiving antenna is almost as intimately 
connected with the transmitter as if a wire joined 
them metallically, although less efficiently to be 
sure. What comes out of the transmitter sets up a 
voltage across the receiving antenna. Naturally, 
the stronger the transmitter, the nearer to the 
receiver, or the higher the receiving antenna the 
greater is the received voltage. 

Here is where we start on our measuring ex- 
pedition. How can we measure the relative 
strength of a transmitter at a given locality? 

HOW RECEIVED ENERGY IS MEASURED 

IN THEORY the problem is about as follows. 
The actual voltage across a given antenna is 
measured by the substitution method. That is, 
a given deflection on a meter is secured from the 
distant station. Then a voltage which can be 
read on another meter is substituted for the 
distant transmitter and when the proper deflec- 
tion is secured the voltages are equal. The process 
may be changed as follows. The given deflection 
is secured. Then a much greater voltage, which 



NOVEMBER, 1927 




4 6 8 10 
RADIATED POWER 

CONDITIONS UNDER WHICH SETS WORK 
Estimates agree that a radio set must have de- 
livered to its antenna a signal strength of be- 
tween one and ten millivolts per meter for 
"good" service. This means that the received 
signal will then be strong enough to over-ride 
ordinary static and local electrical disturbances. 
This curve shows the increase in power neces- 
sary at the broadcasting station to increase the 
range at which a field strength of ten millivolts 
per meter is delivered. Curve A shows the power 
required to lay down this field strength without 
any absorption of the wave; Curve B shows the 
unit power needed to lay down an equivalent 
field strength with all sources of absorption in- 
cluded. Note that at a distance of about 20 miles 
from the station, only about 1.1 units power is 
required for ten millivolts while, with absorp- 
tion, ten units are required to produce the 
equivalent signal 

can be easily measured, is cut down in known 
steps until the same deflection is noted. In this 
manner the field strength of a given station may 
be definitely measured. 

Since the field strength at a given receiver 
varies with the antenna height, the usual basis 
. of comparison is field strength per meter height. 
It is merely the actual voltage measured divided 
by the effective height of the receiving antenna. 
This is expressed in millivolts per meter and is a 
factor which is a measure of the effectiveness of a 
given transmitter at a given locality at a given 
time of day. 

A given number of millivolts per meter will 
produce a certain loud speaker response with a 
given receiver. The more sensitive the receiver 
the greater loud speaker signal will be secured 
from a given field strength, or conversely, a given 



WHAT IS A GOOD RADIO? 

signal may be produced by a weaker field 
strength the more sensitive the receiver. 

What, then, may be considered a good signal? 
Here we are talking dimensions or magnitude. 
What we want to know is the field strength that 
will override static and other interference to 
produce a good lusty loud speaker signal, one 
that will be good, day or night, rain or shine. 

The following table is taken from Dr. Alfred 
N. Goldsmith's paper in the /. R. E. Proceeding 
for October 1926 and shows what may be ex- 
pected from various field strengths. 

NATURE OF 

SIGNAL FIELD STRENGTH SERVICE 

o.i millivolt per meter poor service 
, " fair service 

I0 " " very good service 

I00 " " excellent service 

looo'o " extremely strong 

So far so good. Let us see how powerful a sta- 
tion must be to deliver such a field strength over 
a certain distance. Again quoting from Doctor 
Goldsmith's paper we have the following data. 
ANTENNA POWER SERVICE RANGE 

5 watts ' mile 

50 " 3 les 

500 I0 ", 

5000 " 3 

50,000 loo 

There seems to be some regular progression 
here between the power and the range of station 
in fact a law exists stating that the range of the 
station varies with the square of the power of 
the station. That is, to double the range we must 
quadruple the power. To increase the service 
range three times we actually increase the power 
the square of three or approximately ten times. 
Now quoting Lloyd Espenschied in the Bell 
Svstem Technical Journal (January 1927), we find: 
' Fields between 5 and 10 millivolts per meter 
represent a very desirable operating level, one 
which is ordinarily free from interference and 
which may be expected to give reliable year- 
round reception, except for occasional interfer- 
ence from nearby thunder storms. 

From o. 10 to i millivolt per meter, the results 



50 



100 150 

DISTANCE.MILES 



29 

may be said to run from good to fair and even 
poor at times. 

Below o.i millivolt per meter, reception be- 
comes distinctly unreliable and is generally poor 
in summer. 

Fields as low as o. i millivolt per meter appear 
to be practically out of the picture as far as re- 
liable, high quality entertainment is concerned. 

WHAT POWER DO STATIONS DELIVER? 

FROM a given station the field strength falls 
off according to an inverse law, that is, if we 
double the distance we shall halve the field 
strength: "a 5 kw. station may be expected to 
deliver a field of 10 millivolts from 10 to 20 
miles away and a i.o millivolt field not more 
than 50 miles away." 

In a Bureau of Standards paper, "General H 
port on Progress of Radio Measurements,"(April, 
1924) the following data were published. When 
WEAF was transmitting with 3 kw., its field 
strength at 10 miles was 32 millivolts per meter. 
When KDKA has a nominal power of 10 kw. its 
field at 10 miles was 43 millivolts. 

All of these statements may be expressed 
graphically and the curves on these pages contain 
much meat for thought. What everyone wants is 
good lusty signals from a high quality station, 
day and night, without resorting to regenerative 
receivers to boost the volume at the cost of fidel- 
ity, without being forced to listen to nearby poor 
quality stations riding in on an adjacent chan- 
nel, or without having his program more 
than liberally punctuated with static or ex- 
traneous noises. It is up to broadcasting stations 
to produce a field strength that will insure 
programs and transmission of this desirable 
quality. It is up to design engineers to produce 
receivers that will serve their owners with loud 
speaker signals from the field strengths laid 
down by high quality stations. Mathematics 
alone is not infallible; some experiment and la- 
boratory work must go with it to make certain 
all the factors have been considered. 

Subsequent articles will deal with methods by 
which engineers check up on the soundness of 
their design; methods by which sensitivity, 
selectivity, and fidelity may be measured. 



10.0 
















ST 


MTON WE^ 


F 








(610 Kc.) 








(Bell System Technical Journal) 




en 

1 


[ 




Jan. 1927 






.LI-VOLTS PE 
c 


\ 










RENGTH IN Ml 
p 




V 










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Ift 























HOW FIELD STRENGTH DECREASES 
This curve, from the Bell System Technical 
Journal graphically shows how the field strength 
of WEAF falls off with distance from the station. 
Any receiver, to be subject to tests which indi- 




( 
m e time 



A RADIO "MA?" OF WEAF's SIGNALS 

when WEAF was transmitting from Walker Street, New York this 
York WAF s wer yery famt indee d A 

Mtmd not successfully "pull in" this station. The answer ,s greater 
Poland locatL of broadcastmg stations away from areas of great absorpt.on 



Do You 



a Battery-operated Set? 



Many Fine Types of A-Power Supply Units Are Nou> Available to Convert 
Your Battery -Operated Set to One Which Requires Almost No Attention 

By HOWARD E. RHODES 



NOT so long ago, the only way to heat the 
filaments of your tubes was to use a 
battery. And practically everyone who 
had a radio set had a storage battery; few indeed, 
even in the olden days, used dry cells to light 
their tube filaments unless that was a necessity. 
Then the storage battery passed through a cycle 
of development. The crude battery which radio 
borrowed from the automobile industry was 
dressed up. The case became polished wood or 
even glass and special precautions were taken 
by the makers to keep the acid electrolyte where 
it should be, for this battery was not to 
be housed in the interior regions of a mo- 
tor car but in the parlor of high society. 
And now, to compete with the steady 
old battery come socket A-power units. 
What are they? How much do they cost? 
How many tubes will they supply? Do 
they need regular attention? Can a socket 
A-power unit be installed and be de- 
pended upon to light the filaments of the 
tubes "when, as, and if wanted"? These 
and goodness knows how many other 
questions are being asked by technical 
and non-technical radio folk these days 
as the offerings of 1927 are more and 
more widely announced. 

The owner of a good radio set of some 
years back realizes that the tempting 
new 1927 models, operated directly from 
the light socket, probably are as superior 
to his outfit in convenience and perform- 
ance as Whiskery is to Dobbin. But for 
one reason or another our loyal owner 
decides to keep his receiver. Can't he buy 
gadgets to turn his set into a light-socket 
outfit? Why not, for there are plenty of 
good B socket-power units and a goodly 
number of A socket-power units adver- 
tised? Well, so he can. He can buy a re- 
liable A socket-power unit, a good B 
socket-power unit, a relay switch, and 
there you are complete light-socket 
operation! He has achieved convenience 
which he seems to be pursuing strenu- 
ously. The economics of the change 
is another matter. Of the convenience 
and reliability there is no question. 

Take the case of a set owner who bought a re- 
ceiver a year ago. He may not be quite ready to 
buy a new outfit, but complete light-socket opera- 
tion tempts him. His receiver must be operated by 
these A and B power units without any sacrifice 
in tone quality or volume. If the power units can- 



not accomplish this and for a reasonable length 
of time, without renewal of parts they are not 
worth purchasing. There are, fortunately, many 
A-power units capable of giving as satisfactory 
reception as can be obtained from the un- 
adorned storage battery. 

The storage battery as a source of filament 
power is in many ways an almost ideal device. 
The current it supplies is perfectly steady. Its 
voltage is practically constant during a greater 
part of its discharge, and the slight decrease in 
voltage that does take place as the battery be- 




THE BALKITE A-POWER SUPPLY 

This device will supply filament current to receivers having up to 
eight tubes and it requires practically no attention. Inside the case 
is a transformer and electrolytic rectifier and an electrolytic con- 
denser. The list price is $32.50 



comes discharged does not affect the operation 
of the receiveradversely because tubes of present- 
day design will operate satisfactorily at slightly 
lower than rated filament voltage. Automatic 
A-power units have been developed because the 
public demands convenience. The necessity of 



TABLE I 









MAX. NUMBER 


POWER 




NAME OF UNIT 


PRICE 


TYPE OF 
RECTIFIER 


OF i AMP. 
TUBES UNIT 
CAN SUPPLY 


INPUT 

FROM 

LINE 


CONTAINER 
Lx W x H 


Abox 


$32.50 


Electrolytic 


8 







Balkite A 


32.50 


Electrolytic 


8 


100 


111x613 x8)8 


Electron Electric A 












Regular 


45.00 


Tube 


7 





12} x 71x9 


Giant 


49.50 


Tube 


12 


32 




Marco A Socket Power No. 500 


60.00 


Tube 


10 


47 


Illx7}x9 


Sterling A Supply 


42.50 


Tube 


8 




7 x 11 x8 


Valley Socket A 


39.50 


Tube 


12 


36 


9} x5} x 11 


White A Socket Power 


43.50 


Tube 


9 


39 


111 x7x6j 



charging A batteries is a serious annoyance to 
many radio users. 

TWO GENERAL TYPES OF A UNITS 

THE radio set can be operated from the light 
socket by the use of A and B power units, or 
by designing the receiver to operate with special 
a.c. tubes, receiving their filament current from 
the power mains. The purchaser of a new set 
finds his problem largely solved, for the makers 
of light-socket sets have engineered their sets 
beforehand. It is to the owner of a battery- 
operated set that thisarticleis addressed. 
A power units fall into two classes: 

(a) units using a rectifier and filter sys- 
tem connected through a transformer 
to the a.c. line. (See Table I). 

(b) units using a special storage battery 
in conjunction with a trickle charger. 
(See Table II). 

The various A-power units listed in Ta- 
ble I are all essentially similar in design 
but they differ in minor ways that are 
of interest. All A-power units in Table 1 
must contain ( i ) a step-down transformer 
(to lower the voltage of the line to the 
proper value required by the rectifier 
unit); (2) a rectifying unit (to change 
the reduced a.c. to a sort of d.c.); and 
(3) a filter system (to smooth out the 
product of the transformer-rectifier 
circuit). The filter must eliminate the 
"hum" which is always present in 
unfiltered, rectified a.c. 

Enormous capacity in the filter con- 
denser is necessary to remove this 
troublesome hum. With electrolytic con- 
densers a capacity of 30,000 mfd. can be 
attained in a reasonable space and at 
reasonable cost, and such a large ca- 
pacity as this is necessary for adequate 
filtration. The electrolytic condensers are 
shipped dry and when they are put into 
service, distilled water is gradually 
added to the condenser container. The 
contained chemical, which in some 
cases is potassium hydroxide, dissolves 
in the water. When it completely dis- 
solves, the unit is ready for use. 
These electrolytic condensers require practi- 
cally no upkeep. Every six months or so a small 
amount of distilled water must be added. If the 
user is absent minded and lets the water get too 
low, the unit is not damaged, but indicates its 
need of attention by causing the unit to produce 
an audible hum which is heard in the loud 
speaker. If, "by a set of curious chances," too 
much water is put into the condenser unit, it 
will fail to function properly. Excess liquid can 
and must be removed with a syringe. When the 
water is first put into the condenser can some 
heat will be generated for a short time. 

The Balkite and Abox units both use the form 
of electrolytic condenser discussed above. An 
interesting feature of each of these two outfits is 
that the chemical rectifier electrode is immersed 
in the same electrolyte used for the condenser. 
The outer plates of the condenser act as the 
second electrode of the electrolytic rectifier. This 



NOVEMBER, 1927 



DO YOU OWN A BATTERY-OPERATED SET? 



31 



ingenious scheme achieves very compact con- 
struction. Both these units are supplied with 
external taps which insert resistance in the 
secondary circuit to control the output voltage. 
It is always advisable to use the lowest resistance 
tap that gives satisfactory results. In the Abox 
unit, there is a film of oil on top of the electro- 
lyte which prevents excessive evaporation of the 
fluid. Both units require the addition of a small 
amount of water every six months but do not 
require any other attention. 

Another interesting A-power unit uses the 
Raytheon "A" cartridge a new type of dry 
rectifier. Units of this type are made by Electron, 
Marco, Valley, and Sterling. Some of these use 
one Raytheon cartridge, others two. The Marco 
product, for example, boasts two cartridge recti- 
fiers. A rheostat in the primary circuit allows 
regulation for different loads. A meter on the 
front of the panel simplifies proper ad- 
justment. Inside the box is a relay with 
silver contacts to avoid sticking so 
that the power unit can be controlled 
by the filament switch in the receiver. 

Either one or two Raytheon "A" 
cartridges may be used in the Valley 
A-power unit, depending on the num- 
ber of tubes in the receiver to be sup- 
plied. Full-wave rectification obtains 
with the use of two cartridges. Valley 
suggests using the full complement of 
two cartridges for receivers with seven 
or more tubes. A single cartridge will 
suffice for more modest receivers. This 
Valley device also uses an electrolytic 
condenser to smooth the output of the 
cartridge rectifiers. Since it is shipped 
without liquid, the dry chemical may 
rattle in the condenser can and excite 
some curiosity on the part of the pur- 
chaser. The addition of water, accord- 
ing to directions, makes all things as 
they should be. Between the rectifier 
and filter system is the control rheostat 
which provides sufficient regulation for 
various loads imposed by the receiver. 

The A-power unit from Sterling uses a 
single Raytheon cartridge, is equipped 
with ar Automatic filament circuit re- 
lay, a control rheostat, and a meter to 
facilitate the correct voltage adjust- 
ment. 

The White unit among those listed 
in Table 1 is the only one on which 
we have information which uses a 
Tungar or Rectigon tube as a recti- 
fier. The transformer in this device delivers about 
8 volts to the plate and about 2 volts to the fila- 
ment of the rectifier tube. The rectifier tube has 
a rating of 2 amperes, which, according to its 
manufacturers, is conservative; the unit, when 
operating under normal loads, should therefore 
have a long life. The filter circuit in this device, 
besides the usual electrolytic condenser, contains 
a 4-henry choke to assure complete elimination 
of hum. A calibrated rheostat to control the 
output is connected between the tube and filter 
system and the meter scale on the front panel 
enables the user to adjust the unit accurately 
and with ease. A six-foot cord with a pendant 
switch is supplied to control the a.c. input. 

YOU WON'T RECOGNIZE THE STORAGE BATTERY 

A LL the units listed in Table I are grouped 
** there because they provide a source of A 
supply by utilizing a rectifier and filter system, 
while those of Table II combine a storage 
battery and trickle charger. There are many 
radio users who are convinced that the ideal 
A-socket power unit is one that is innocent of 
liquid of any sort. An unfortunate experience 



with the old storage battery may have instilled 
this dislike of an A-supply involving liquids. 
But as radio has developed and the inevitable 
and fortunate process of refinement has occurred, 
ingenious ways have been found to mould the 
storage battery into a highly desirable product 
indeed. Another(school of manufacturing thought 
therefore has worked along these lines. They 
have taken the storage battery, designed it 
exactly to fit modern radio needs, and in the 
process have succeeded in producing a unit 
which has none of the disadvantages always 
quoted against it. Since any of the two distinct 
types of socket-power A units listed in Tables 
I and 1 1 supply satisfactory A potential to the re- 
ceiver, and differ largely in the electrical means 
used to produce the direct current for the tube fila- 
ments, whether one chooses one type or the other 
is entirely a matter of personal preference. 




THE VESTA GLASS ENCASED A-POWER UNIT 

This is a combination storage battery and trickle charger combined 

with a relay so that its operation is entirely automatic. A distinctive 

feature is that the entire unit is enclosed in a moulded glass case so 

that all the parts are visible. The list price is $47.50 



Storage battery makers, since radio became 
popular, have sought to reduce the routine at- 
tention demanded by the storage battery. To- 
day's battery requires only the occasional ad- 
dition of distilled water. Keeping the battery 
"up" is automatically accomplished by a trickle 
charger. By a study of the demands on storage 
batteries used by a wide variety of radio owners, 
sufficient data have been collected to accomplish a 
storage battery-trickle charger combination which 
needs only slight attention. 



The principles of operation of this type of de- 
vice have not been changed, but this year many 
important improvements have been made which 
insure satisfactory service and almost entire 
freedom from user attention. Unusually thick 
plates, especially designed vent caps, built-in 
"state of charge" indicators, conveniently lo- 
cated controls to vary the charging rate, and 
special cell construction to insure long life in 
trickle-charging service all contribute to make 
the combination trickle charger and storage 
battery a convenient and satisfactory A socket- 
power unit. 

Let us discuss some of the points of interest in 
these devices. The Acme A-power unit, type 
APU-6, is designed to supply 8 to 10 tubes. The 
battery unit can be charged at two rates: 5 and 
ij amperes. This wise provision permits adjust- 
ment of the unit to take care of the demands of a 
receiver with many tubes, or the lesser 
current requirements of a set with 
fewer tubes. 

The Westinghouse"Autopower" has 
much to commend it. Our friends in 
East Pittsburgh have combined in a 
compact unit both a storage battery 
and an efficient trickle charging de- 
vice, the latter developed during the 
last year. This rectifier, which is the 
heart of the charger, is interesting 
enough to merit a slight digression 
Several years ago, it was found possi- 
ble to make a solid body of matter 
conduct electricity more freely in one 
direction than in the opposite one. This 
was the origin of Rectox, the trade 
name of the rectifier used in the "Auto- 
power" and some units by other mak- 
ers, operating under Westinghouse 
licenses. The first materials to show 
this property offered three times as 
much resistance to the passage of elec- 
tric current in one direction as in the 
other. The present Rectox units, de- 
veloped after considerable research, 
have increased this resistance ratio of 
3 to i to as high as 20,000 to I in the 
final units. The life of this rectifier unit 
is said to be indefinite. 

A special clip on the front of the 
"Autopower" makes it possible to ob- 
tain three different rates of trickle 
charging. In addition, a "booster" rate 
can be used to revivify the battery 
if the receiver has been used for an 
excessive length of time. (One thinks 
of the nj- hour continuous Lindbergh broad- 
cast of last June!) The unit contains a relay, 
which, when the set is turned on, automat- 
ically disconnects the a.c. from the trickle 
charger and connects it instead to two leads 
terminating in a plug on the side of the "Auto- 
power" unit into which the connecting cord of a 
B-power unit is connected. When the radio re- 
ceiver is turned off, the relay automatically closes 
the trickle-charger circuit and the battery begins 
to charge. At the same time, the relay opens the 



TABLE II 



NAME OF UNIT 


WATTS 
INPUT 


PRICE 


MAX. NUMBER 
OF TUBES UNIT 
CAN SUPPLY 


TYPE RECTIFIER 
USED IN 
CHARGER 


SIZE 
Lx WxH 


Acme A power 


_ 


$35.00 


10 


Tube 


Ilix7x9i 


Autopower 
Basco A power 


22 
35 


35.00 
40.00 


10 
12 


Copper oxide 
Tube 


11 x6f x9} 
125 x 5J x 10 


Compo 


26 


42.50 


8 


Tube 


105 x5j x8} 


Exide Radio Power 


17 


31.90 


10 


Tube 


11 x5," n x9 


Philco A Socket Power (603) 




32.50 


6 


Electrolytic 


12! x 9$ x7j 


Unipower AC-6-K 


24 


39.50 


10 


Electrolytic 


!Hx7&xlO 


Universal 





32.50 


8 


Dry disk 


8ft x 8 x 7J 


Vesta A Power 





37.50 





Dry rectifier or 


9J x 7J x 9j 










electrolytic 




Greene-Brown 


29 


30.00 


10 


Tube 


8f x 31 x 10i 



32 



RADIO BROADCAST 



NOVEMBER, 1927 



circuit to the B-power unit so that this unit is 
automatically disconnected. The "Autopower" 
requires no attention except the occasional ad- 
dition of distilled water to the battery. 

WHAT THE UNITS CONTAIN 

THE Basco A-power unit contains in a single 
case the storage battery, the rectifier, an 
automatic relay (similar to the type just de- 
scribed above), an emergency switch, trans- 
former, fuses, and a terminal board. The battery 
is an all-glass Exide unit with a capacity of 45 
ampere hours. It is equipped with colored in- 
dicator balls to show the condition of charge. 
A thin film of oil on the surface of the electrolyte 
prevents undue evaporation and also prevents 
spraying and corroding of battery terminals. 
This battery has a large water space and the 
ordinary user will not have to add distilled water 
oftener than every half year. The Basco A unit 
is connected to the receiver just as if it were an 
ordinary battery and when the receiver is turned 
on, the current from the battery flows to the 
tubes and at the same time passes through an 
automatic relay which closes a circuit and makes 
1 10 volts (for your B-power unit) available at a 
plug on the side. When you are through using 
the set, turn off the switch. The relay automati- 
cally opens the B-power unit circuit and puts the 
battery on charge. A Raytheon "A" rectifier is us- 
ed as the charging rectifier. This rectifier has the 
advantage that its rate of charge automatically 
decreases as the battery becomes charged. Danger 
of overcharging is decreased. The "emergency" 
switch mentioned above is used to recondition the 
battery after it has stood idleforsome time. Turn- 
ing this switch recharges the battery at a high 
rate and inconvenience is reduced to a minimum. 
A 35-ampere hour battery in a composition jar 
with a special cellulose moisture-proof pad on 
top of the plates and a paste electrolyte are 
features of the Compo A-unit. An eye-dropper 
full of distilled water in each cell about every four 
months is all the attention the unit requires. 



Three rates of trickle charging are available: 
0.2, 0.4, and 0.6 amperes. 

The Exide model jA 6-voIt A-power unit is 
designed to supply constant voltage direct cur- 
rent for the operation of the filaments of the 
tubes in any standard radio set. It comprises a 
storage battery and trickle charger with three 
taps, each affording a different charging rate. 
This rate depends, of course, on the number of 
tubes in the receiver and the number of hours the 
set is used. The battery is a standard Exide unit 
of excellent design and construction and con- 
tains ample space for excess electrolyte over the 
tops of the plates, thus making necessary the 
addition of distilled water only once or twice a 
year. The makers recommend it be used with the 
Exide master control switch which contains an 
extra plug for the a.c. supply for a B-power unit. 
The unit has a visible charge indicator consisting 
of two small colored balls so that the condition of 
the battery can be told at a glance. The entire 
unit is contained in a nicely finished sheet steel 
enameled case, fitted with two carrying handles. 

The Philco A socket-power unit also affords a 
dependable source of filament potential. Philco 
has refined this unit in many ways during the 
last year to make it entirely fool-proof and eco- 
nomical in operation. The model 603 A power unit, 
listed in Table II, consists of a high-efficiency 
transformer and rectifier with a battery espe- 
cially designed for trickle charging service. The 
battery has unusually thick plates and separators. 
Spray-proof construction, preventing the leakage 
of electrolyte from the battery, and the built-in 
state-of-charge indicator, are two important im- 
provements. These heavy plates and separators 
insure long life and freedom from the danger of 
internal short-circuit. Without the built-in 
Philco indicator there would be no simple means 
of determining the condition of the battery ex- 
cept through the use of a hydrometer and when 
it is used there is always the possibility that some 
acid will be spilled, incurring the righteous wrath 
of the housewife. Special vent-caps have been 




A PHILCO UNIT 

This Philco unit incorporates several interesting features among which are a visible indicator of the 
state of charge of the battery and special vent caps on the battery which absolutely prevent any 
.acid from leaking out of the battery. These vent caps do not have to be removed in order to add 

water to the battery 



incorporated in the Philco units which make 
possible the addition of water to the battery 
without removing them. And water need not be 
added to these cells oftener than twice a year. 
Water will flow down these vent-caps, but it is 
impossible for any of the enclosed acid to leak 
out. In normal operation the vent-caps need 
never be removed. Philco units employ an 
"economizer" which permits the user to adjust 
the charging rate to the lowest current consump- 
tion which will, at the same time, keep the bat- 
tery properly charged as shown by the visual 
indicators. By using the lowest possible rate, 
gassing of the electrolyte is prevented, and this re- 
duces the frequency with which water need be 
added. Three charging rates are available with a 
"booster" rate for emergency use. The batteries 
are in a glass container. Philco units can be had 
for operation on 25- 30- 40- 50- or 60- cycle a.c. 
Type A6o3 is designed to supply up to six tubes 
and type A-36 is designed to supply up to ten 
tubes. The latter type contains a dry trickle 
charger which provides three rates: 0.25, 0.5. 
0.26 amperes and a i.o-ampere rate for booster 
service. 

The Unipower type Ac-6K provides, accord- 
ing to its makers, three unique features. First, a 
"Kathanode" cell construction which insures 
long battery life; secondly, an automatic cut-off 
in the rectifier cell which suspends charging 
if the user fails to add water when necessary, and 
third, five charging rates with a high rate of ij 
amperes meeting the requirements of all grades 
of receivers. 

In the " Kathanode" design, porous glass wool 
mats are fitted against the positive plates to 
prevent the shedding of active material which 
frequently occurs if the battery is overcharged. 
The glass mats, by capillary action, draw fresh 
acid to the plates, increasing efficiency. The Uni- 
power, cased in rubber, contains three " Katha- 
node" constructed battery cells, a rectifier cell, 
a transformer, as well as the essential switches, 
terminals, and connections. All these cells are 
watered at once and the rectifier is designed so 
that when the level of electrolyte exposes the 
tops of the cell plates, the charging current is 
automatically cut off until water is added. The 
makers feel this safeguard is essential to the 
proper operation of the battery. On the front of 
the unit, a dial regulates the charging rate, which 
ranges from 0.25 to 1.5 amperes in five steps. 

A Rectox dry disk rectifier is used in the Uni- 
versal A-power unit. The 36-ampere-hour battery 
is assembled in a three-compartment glass jar 
with mounted hard rubber covers. This A-power 
unit has a visible state-of-charge indicator, and 
the whole device is supplied in a steel container. 

One of the first battery-trickle charger com- 
binations received in the Laboratory in which 
glass was the container was the handsome Vesta 
A-power unit. Vesta now makes two A-power 
units, one containing an electrolytic trickle 
charger and the other a dry trickle charger. A 
visible charge indicator shows the state of the bat- 
tery; when the three colored balls float at the top 
of a small compartment, the battery is fully 
charged and as the charge decreases, one ball 
after another gradually sinks to the bottom of 
the compartment. The Vesta unit has a socket 
into which the a.c. plug for the B socket-power 
unit may be plugged. 

So the A-power devices of 1927 look and per- 
form very differently from the indiscriminate 
units with which the radio user of some years 
ago was content. If a variety of A-power devices 
are offered the purchaser and he does not know 
what type to use, he should ask his local dealer to 
install them in his home so he can easily choose 
the one which best fits his own needs and his 
local conditions. 



Rtl 



C2 



R4 



R7 



L3 



C1 




R 12 I I I Z RADIO BROADCAST Photograph 

(UNDER COIL) 

A NEW BROWNING-DRAKE RECEIVER 

The new Browning-Drake receiver shown above is to be described constructionally next month. It has been designed for complete 
a.c. operation although batteries may be used if desired. This first article discusses the various a.c. tubes suitable for the purpose 




A Discussion of the New A. C. Tubes and How They May 
Be Incorporated in a New Design Browning-Drake Receiver 



WITH the availability of really good a.c. 
tubes, another and important step 
toward the ideal radio set is made. 
With the a.c. tube, no storage battery or A-power 
unit is required. All that is necessary is merely 
a compact little transformer for decreasing the 
line voltage to a suitable operating value. As 
far as actual performance is concerned, the new 
a.c. tubes are essentially the same as the well- 
known 20I-A or JOI-A type tubes. The person 
with a set equipped with standard tubes will 
not improve the performance of his set by chang- 
ing it over for a.c. tube operation. If his storage 
battery, charger, and tubes are in good condi- 
tion, there is nothing to be gained by such a 
change. If, however, the batteries have about 
run their useful life, or if the charger has died of 
old age, the new tubes offer a number of worth- 
while attractions to the home constructor. First, 
they open new fields for experiment; second, 
they enable him to build a completely lamp- 
socket operated receiver for less money than a 
battery operated receiver with its associated 
storage battery and charger, and at the same time 
there results a receiver somewhat simpler to 
maintain. 

Once a few of the little tricks of the use of a.c. 
tubes are acquired one will have no difficulty in 
constructing any of the popular circuits for a.c. 
operation or in replacing old tubes in any 
standard receiver with new a.c. tubes. Perhaps 
the best way of acquiring this knowledge is to 
carefully follow the details in connection with 



By JAMES MILLEN 

the construction of some popular circuit for use 
with the new tubes. With this in mind, we have 
selected the Browning-Drake as one of the most 
popular receivers which has been described in 
past issues of RADIO BROADCAST, and have re- 
designed it not only for complete a.c. operation, 
but also to incorporate the latest ideas on layout, 
audioarsplification, and other slight modifications 
of the original Browning-Drake circuit. Further- 
more, the set has been so designed that it may, if 
desired, be wired for battery operation where the 
constructor is not so fortunately situated as to 
have a.c. on tap. The photograph gives an 
idea of how the completed receiver looks. Com- 
plete construction data on this set will be given 
in the next article. In this article we will consider 
some of the general problems involved in the 
use of a.c. tubes. First of all let us consider the 
different a.c. tubes available for all but the last 
audio stage. The last audio, or power tube, be 
it of the 112, 171, or 210 variety, may be oper- 
ated on raw a.c. just as well as on batteries. No 
special a.c. tube is required, therefore, in the 
last audio stage. 

It will be seen from the table on the next page 
that the a.c. tubes may be divided into two gen- 
eral types, i. e., those using a low-voltage high- 
current filament, and those having a separate 
heater element. The heater type tubes are better 
suited as detectors than the filament type, but 
either type are about equally well suited as radio 
and audio amplifiers. Since the heater tubes are, 
in general, more expensive and have shorter lives, 



it is advisable to restrict their use to the detector 
socket. 

The different filament heating transformers 
available are mostly designed for direct opera- 
tion with the RCA-Cunningham tubes without 
the use of rheostats or other resistors. The volt- 
age taps on some of the transformers available 
at present are: 



MANUFACTURER 
Amertran 
Dongan 
General Radio 
Modern 
National 
Silver-Marshall 
Thordarson 



TAPS (IN VOLTS) 
.5,2.5. 5-0 
.5. 2.5, 5.0 
.5, 5-o, 7-5 
.5,2.5, 5.0 
.5, 2.5, 5.0 
.5,2.5, 5-o 
5, 2.5, 5.0 



2, 



When a.c. tubes of other manufacturers are 
used with transformers having the proper taps 
for the RCA-Cunningham tubes, special rheo- 
stats made by General Radio and Carter should 
be used in the low-voltage transformer leads. 
When tubes of the Armour-Van Home type are 
used throughout, then two short lengths of re- 
sistance wire with a total resistance of about o. I 
ohms should be inserted in the leads to the 
detector and audio amplifier tubes so that they 
operate at a slightly lower voltage than the radio- 
frequency amplifier tube. Several manufacturers 
make special resistors for just this use. 

Where the Kellogg tube is used only as a de- 
tector, the 2.5-volt filament transformer winding 



34 



will be found just right. Where Kellogg tubes are 
used throughout, then the 1.5- and 2.5-volt wind- 
ings should be connected in series (that is, so 
that their voltages add rather than subtract) 
to give 4 volts which may be dropped down to the 
desired 3 volts with a suitable rheostat or fixed 
resistor. The filament voltages required by any 
of the tubes are far from critical and the tubes 
will be found to perform excellently with voltages 
considerably below the rated values. Operating 
the detector at a lower voltage often results in 
almost complete elimination of any hum. If 
the heater voltage of a uv-22y detector is exces- 
sive, the set will cease to regenerate, and, in fact, 
practically stop operating. Generally, about 2.2. 
volts seems to work best with the 22y's when used 
as detectors and a six-inch length of wire from 
an old-ten ohm rheostat, in series with one of 
the 2.5-volt transformer leads, will give this lower 
voltage. 

The 1.5- and z.j-volt transformer windings 
should not be center-tapped as potentiometers 
located close to the tube sockets are necessary for 
the best results. The 5-volt winding for the 
171 or the 7. 5-volt winding for the 210, however, 
may just as well have a center tap and thus 
eliminate the need for one potentiometer. The 
detector and the power-tube filament circuits 
should be wired with No. 18 equivalent rubber 
covered twisted wire. The proper size wire for the 
radio and first audio stages, containing high- 
current tubes, may be determined by estimating 
the total current drawn by these tubes from the 
table of characteristics and then selecting a wire 
that will carry such a current from the table 
below. In the case of the Browning-Drake re- 
ceiver using RCA tubes, No. 18 may be used, 
but if the Van Horne-Armour type tubes are 
used, then No. 16 will be necessary. The follow- 
ing table gives the current-carrying capacity of 
rubber covered copper wire: 



WIRE SIZE 

14 
16 
18 
20 



CURRENT 
1 1 amperes 

6 

3 

I.J 



THE R. F. AMPLIFIER 

CITHER the heater or the filament type of 
^ tube will work well in the radio stages, but 
because of its longer life, lower cost, and simpler 
connections, the filament type is generally to be 
preferred. There is, however, one real advantage 
that the heater types have over the filament 
types when used with some cir- 
cuits, and that is lower inter- 
electrode capacity, which often 
facilitates neutralization. The fila- 
ment type a.c. tube may be 
employed in the r.f. stage of a 
Browning-Drake receiver with 
materially improved results over 
those obtained with the customary 
199 type tube. 

While frequently no negative 
grid bias is employed on the r.f. 
tubes in a battery operated re- 
ceiver, the use of this bias is es- 
sential with the a.c. filament type 
tube. This biasing voltage may 
be obtained from a C battery or 



RADIO BROADCAST 

by utilizing the voltage drop across a suitable 
resistor which can also provide the bias for the 
first and second audio-frequency stages. 

The optimum r.f. tube plate voltage for mini- 
mum hum does not seem to be at all critical and 
the 6-5-volt tap on the average B supply unit 
gives as good results as any, with less tendency 
for the radio-frequency stage to oscillate than 
when the go-volt terminal is used. The C bias 
on the r.f. tube should be a little more negative, 
for a given plate voltage, than on the a.f. stages. 
The use of a somewhat lower plate voltage on 
the r.f. tube than on the a.f. tubes permits the 
use of the same C voltage on both the audio- 
and radio-frequency tubes. 

The use of a.c. tubes and a B power unit make 
two of the forms of volume controls considered 
more or less standard with battery operated 
receivers the r.f. filament rheostat and the 
variable series resistor in the r.f. plate circuit 
unsuited for the electric receiver. There are, 
however, at least two other systems of volume 
control which will give satisfactory results. One 
is a variable antenna coupling coil, and the other 
is a variable resistor across the primary of the 
r.f. transformer. By this means it is possible to 
control the volume by varying the r.f. input to 
the detector circuit. 

A potentiometer across the filament circuits 
of both the radio and first audio stages must be 
employed. As the voltage is low, this unit may 
be a 30-ohm rheostat with a third connection 
made to the "open" end of the winding. As this 
potentiometer may, from time to time, require a 
minute change of adjustment, it is well to locate 
it in some convenient place on the sub-panel. 
The potentiometer should not in general be 
mounted on the front of the panel, as for best 
results it must be hung directly across the fila- 
ment leads at about an equal electrical distance 
from all the tubes. The adjustment of this poten- 
tiometer is quite critical, and a very slightly 
different setting is frequently required at night 
than during the day in order almost completely 
to eliminate all the hum and the hum can cer- 
tainly be reduced to a very low order if the re- 
ceiver is carefully constructed and adjusted. 

A. C. TUBES IN THE AUDIO AMPLIFIER 



NOVEMBER, 1927 

of the ux-226 (cv-^2(>) tubes with 90 volts on 
the plate, the grid bias should be adjusted until 
the drop across its terminals, as measured with a 
high-resistance voltmeter, is about 6 volts. In 
the case of the Browning-Drake receiver to be 
described in detail next month, a fixed 5OO-ohm 
wire-wound resistor is used to obtain C bias and 
this value of resistance is just right. Any of the 
several different forms of audio amplification may 
be employed with excellent results. 

Where the grid bias for several stages is ob- 
tained by taking the voltage drop across one re- 
sistor, as in this case, then the use of a "grid 
return filter" in each stage is recommended and 
such filters have been used in the a.c. Browning- 
Drake receiver. These filters merely consist of a 
o. i-megohm resistance and a i-mfd. condenser 
connected so as to prevent any of the audio- 
frequency currents from flowing through the 
grid bias resistance. In the last or power stage, 
the 171 is recommended as the tube best suited 
for home use. A 2ooo-ohm wire-wound resistor 
will automatically provide the proper grid bias 
for this tube regardless of the plate voltage, 
within reasonable limits. A loud speaker pro- 
tective device to eliminate the direct current 
from the loud speaker windings should be em- 
ployed. 

THE DETECTOR 

\ A /HILE either form of a.c. tube may be used 
* 'as a detector, the uv-22y type of heater 
type tube has several advantages over the fila- 
ment type. First, the a.c. hum can be, for all 
practical purposes, entirely eliminated. The 
hum from a filament type a.c. tube is not what 
could in any way be termed objectionable, yet, 
it is there. The heater tube may be used with 
either a grid-leak condenser arrangement or with 
C bias, whereas, the 226 type of tube, while it 
will function quitewell witha grid-leak condenser, 
is better suited for plate rectification. Plate recti- 
fication, however, is not as sensitive as the grid- 
leak condenser arrangement and its use in con- 
nection with an all a.c. operated receiver also 
leads to other complications. The Kellogg a.c. 
tube may be used as a detector with excellent 
results. 

In using the heater type tube as a detector, 



AS THERE is nothing to be gained by the either a negative or a positive bias of about 40 

* * ncp r\f fhp mnrp pvnpticivp hpatpr t\/np tiihp \;r\ltc nr art Qhriiil/i HP 'irMiltp/l tn tVin hpitur n!p_ 



use of the more expensive heater type tube 
in the first audio stages, the filament type is to 
be recommended. As already mentioned, the one 
potentiometer and grid bias resistor serves 
both the radio and the audio stages. In the case 



A. C. TUBES 
Heater Type 


NAME 


Ef 


If 


Ip 


R P 


M u 


Gm 


E p 


E * 1 


0-327 


2-5 


75 


4.2 


8600 


7-8 


905 


90 


-45 


UY-227 


2-5 


.65 


3-5 


10350 


8.7 


860 


90 


-4-5 


McCullough 


3.0 


.0 


4.2 


9400 


8.6 


870 


90 


-45 


Sovereign 


3.0 


5 


4.6 


9100 


8.5 


935 


90 


-4-5 1 


Marathon 


5-5 


.0 


4.2 


9500 


7-3 


775 


90 


-4-5 ! 


Arcturus 


15.0 


0-35 


3 ' 


12150 


10.5 


870 


90 


-4-5 I 


Magnatron 


2-5 


1.50 


4.6 


8700 


9-3 


1070 


90 


-4-5 i 


Filament Type 


cx-326 


5 


1.05 


4.6 


9000 


8.5 


935 


90 


-4-5 i 


UX-226 


5 


1.05 


4-4 


9150 


8.7 


950 


90 


-4-5 1 


Armor 


.0 


2.4 


3.8 


I I2OO 


7.8 


690 


90 


-4-5 i 


Van Home 


.0 


2.0 


44 


9000 


9.0 


IOOO 


90 


-4-5 


CeCo 


5 


1.05 


2.8 


14200 


9.2 


730 


90 


-4-5 


Magnatron 


-5 


1.05 


4.0 


10800 


8.8 


830 


90 


-4-5 


Ef = Filament Volts l p = Plate Current 


E P = Plate Volts R p = Plate Resistance 


E K = Grid Volts M u = Amplification Factor 


If = Filament Current G m = Mutual Conductance 



volts or so should be applied to the heater ele- 
ment by means of a potentiometer. In some in- 
stances a positive bias seems best and in others, 
a negative, and either of these biases are readily 
obtainable from the 4O-volt tap supplying C bias 
to the power tube or the plus 
45-volt tap for the detector. The 
adjustment of this bias voltage 
is not at all critical, and once 
set, will require no further atten- 
tion. In fact, a fixed resistor with 
center tap, such as the type 438 
General Radio, will serve the pur- 
pose excellently. This resistor is so 
designed as to mount directly on 
the terminals of the detector tube 
socket. 

In a second article which will 
appear next month, constructional 
details and adjustment sugges- 
tions on the a.c. Browning-Drake 
receiver will be given. 







Our Readers Suggest 



9 9 



C'p'HESE two pages' are reserved for the many in- 
-I teresting contributions from our readers, some of 
whom may have run across many ingenious , ideas in 
the operation of broadcast receivers and accessories. 
These pages will appear regularly in RADIO BROAD- 
CAST and all contributions accepted will be paid /co- 
at our regular rates. In addition, each month, a prize 
of }io will be paid for the best contribution published. 
Contributions are especially desired about changes 
and simple adaptations dealing with ready-made re- 
ceiving sets and accessories. Those who have made 
their own receivers are, in a sense, experts, and are 
usually well aware of the possible improvements in 
the use of their own equipment. Each contribution will 
be published as the writer prepares it, telling how he 
solved his problem, to which will be added some com- 
ments from the staff. Address ail contributions to The 
Complete Set Editor, RADIO BROADCAST, Garden 
City, New Torf(. THE EDITOR. 



Rewiring an Atwater Kent Receiver 
for A. C. Tubes 

THERE seems little doubt in the minds of en- 
gineers that the alternating-current tube will 
eventually find a place in the majority of radio 
receivers. It is in anticipation of this eventuality 
that RADIO BROADCAST has already devoted 
considerable space to the problems of A battery 
elimination and the characteristics of a. c. tubes. 
We are interested in the following description of 
how a reader, Henry March, of New York, altered 
a popular type of receiver for a. c. operation, 
necessitating few and simple circuit changes. He 
writes: 

"It has been my pleasure to discover that the 
Atwater Kent Model 35 receiver can be easily 
adapted to a. c. operation through the use of a. c. 
tubes. I presume that the same simplicity of con- 
version holds true for many other receivers a 
fact that may interest your readers. 

"I rewired my receiver for Arcturus tubes (type 
28 amplifier, type 26 detector, and type 30 power 
tube), choosing these tubes because of the fact 
that they plug into the four-prong socket which 
is standard equipment on practically all receivers 
wired for storage battery tubes. Thus no addi- 
tional filament wiring or special sockets are 



required greatly simplifying the necessary 
changes, which are illustrated clearly in the ac- 
companying diagrams. Fig. i shows the original 
wiring in the receiver. The parts of the circuit to 
be changed have been drawn in heavy lines. 
Fig. 2 shows the circuit with the changes made. 
"All grounds have been eliminated from the fila- 
ment circuit. The lower terminals of all r. f. and 
a. f. secondaries, excepting that of the power 
tube, have been grounded. The detector grid re- 
turn to the potentiometer has been eliminated, 
and the return is now effected through a 4.5-10 
Q.o-volt C battery, positive to the grid. Detector 
C minus is connected to the B minus post. The 
plus terminal of the main C battery also con- 
nects to B minus. Minus 1.5 C battery is 



STAFF COMMENT 

AS OUR contributor suggests, a. c. tubes of 
this type (the characteristics of the Arc- 
turus tubes are given on page 34) may be used 
in many receivers after relatively simple changes 
have been made. However, the operation of alter- 
nating-current tubes is essentially a complicated 
proposition, and it is recommended that readers 
secure specific information on the changes re- 
quired in their particular receivers before pro- 
ceeding with the alteration. This information can 
generally be secured from the manufacturers of 
the tubes selected, and from the technical de- 
partment of this magazine. 

However, a few generalities may be laid down 



Ant. 



Gnd 




C-1.5 



B+ 67Sj C-22H. B+ 180 



FIG. 2 



grounded (supplying the r.f. tubes), while 22.5 
minus runs to the power tube in the usual manner. 
A Centralab modulator is connected across the 
secondary of the first audio transformer as a 
volume control. 

"The a. c. filaments are operated from an Ives 
step-down 'toy' transformer (type 204) at the 
14.5 volt tap. All plate voltages remain the same 
as in the d.c. set, excepting that 180 volts is 
applied to the output power tube, increasing the 
possible undistorted power output of the re- 
ceiver." 



Ant. 



Gnd. 




FIG. I 



for the adaptation of d. c. receivers to a. c. opera- 
tion. Much of this is covered diagramatically in 
the accompanying circuits. 

All grounds must be eliminated from the fila- 
ment circuit. Ground all secondaries (filament 
side) having the same negative bias. A bias of 
minus 1.5 to 3 volts is generally applied to all r. f. 
grids. 

Run the two filament wires as close together as 
possible, lacing or twisting them when conve- 
nient. Be sure that all plus filament posts are 
connected together. Connect minus B to what 
previously were the positive posts. Connect the 
r. f. and the a. f. C plus and the detector C 
minus to B minus. 

Eliminate all filament rheostats and potenti- 
ometer r. f. controls. It is not practicable to use 
these forms of volume and sensitivity control 
with a. c. tubes. With the potentiometer device, 
sensitivity is governed by varying the bias on 
the r. f. tubes which, with a. c. tubes, would in- 
troduce hum at certain adjustments. A 250,000- 
ohm variable resistor connected across the r.f. 
secondary preceding the detector tube is a pre- 
ferred volume control. 

Receivers wired for four-prong base a. c. tubes 
can be used with d. c. tubes at any time, merely 
by substituting an A battery for the transformer. 
No other changes are necessary for d.c. opera- 
tion of such a receiver. 



36 













+ 90V. 


1 








S 










Minus lead inside 


+ 45V. 


'i 


of Eliminator 




D 




'U. 


| 1000 Q 




1.0 mfdT" 


* -o c 






(40V. at 40m A.) 



FIG. 3 

C Bias from a Mayolian Socket 
Power Unit 

B -SOCKET power units in the future will 
undoubtedly incorporate extra resistors 
making it possible to secure C bias for at least 
the power tube. It is not difficult to incorporate 
this feature in the average power unit along 
the lines described by a contributing reader. 
James J. Corrigan, of Des Moines, Iowa: 

"I have a Mayolian B power unit, the utility 
of which I have doubled by adding an extra re- 
sistance and bypass condenser. The drop across 
the resistance supplies the C voltage to my power 
tube. 

"The lead to the negative binding post is 
broken at 'X' inside the case (Fig. 3). A 1000- 
ohm, two-watt resistor is connected in the break 
and by passed witha i.o-mfd. condenser. The post 
marked B minus connects as usual to the receiver, 
while the C bias voltage is tapped in the elimina- 
tor side of the resistor. A forty-volt C battery 
is supplanted by this means. 

STAFF COMMENT 

T'HIS is a simple and practical method of C 
battery elimination, readily applicable to all 
eliminators giving voltages, under load, in excess 
of 180. The C voltage is necessarily subtracted 
from the B voltage, and the compromise is some- 
times undesirable. If your eliminator has a no- 
load potential of about 250 volts, C elimination 
is quite worth while. Many B-socket power units 
fill the bill. Among them are: Kodel, Burns, 
Greene-Browne, Kellogg, and General Radio. 

However, the use of a fixed resistor is not 
recommended as it is almost impossible to secure 
the right bias. It is suggested that a variable 
resistor, connected as shown in Fig. 4, be used 
instead. Amsco Products manufacture a zero to 
2ooo-ohm variable resistor known as a Duostat, 
made especially for this purpose. It is equipped 
with two variable arms, making it possible to 
secure two C bias potentials, one for the power 
tube and one for the other a. f. tubes Each arm 
of the Duostat must be bypassed with a i.o- 
mfd. condenser. Other variable 2OOO-ohm C bias 
resistors are made by Carter and 
Electrad. 

A rough adjustment of the bias 
potentials can be made by ear. 
However, a much more scientific 



RADIO BROADCAST 

job can be done with the aid of a small milli- 
anipere meter, reading up to 25 milliamperes. 
This should be placed in the plate circuit of the 
tube on which the bias is being adjusted. The 
variable arm is moved until, on a loud signal, the 
needle is motionless, or practically so. Any 
movement of the needle is an indication of dis- 
tortion. If the needle kicks up, turn down the 
resistance (lowering the C bias); if the needle 
kicks down, increase the resistance. 

This careful adjustment is generally made only 
on the output tube. The meter is connected in 
series with the loud speaker, or the primary wind- 
ing of the output device if such is used. As the 
power handled in the preceding tubes is generally 
small, a rough adjustment by ear is adequate. 

Getting High Notes from the 
Resistance-Coupled Set 

1HAVE a Ferguson Model 12 receiver, in which 
were incorporated three stages of resistance- 
coupled amplification. I operated this set in con- 
junction with a Western Electric 540 AW cone 
loud speaker. While the tone quality of this com- 
bination was distinctly superior to that of the 
average set, there was, at times, a disconcerting 
rumble on low notes, which quite counteracted 
my pleasure in the unusual reproduction of these 



-0 + 180V. 




0+ 90V. 



0+45V. 



O- B 



0-J2T 
0-X 



FIG. 4 

low frequencies. There seemed to be a resonance 
point in the output system in the neighborhood 
of fifty cycles. A friend of mine has an impedance- 
coupled set, which, while quite free from the 
particular disturbance I mention, is distinctly 
partial to higher notes. It occurred to me that a 
compromise between resistance and impedance 
coupling might be ideal in my particular case. 

Upon the advice of an experienced fan, 1 
removed the coupling resistor from the second 
audio stage, and ran two wires from the prongs 
to the primary of an old audio-frequency trans- 
former. 1 left the grid leak exactly the same as 
when resistance coupling was used (See Fig. 5). 

The result is most gratifying. There is no 



UX201-AorCX301-A UX201-Aor 
I UX240or,CX340 n CX301-A'. 



Choke 
Coil 



UX 171 or 
CX371 




NOVEMBER, 1927 

longer any rumble on the troublesome notes, and 
it seems to me that the speaking voice is cleared 
up a bit ... it is more natural. Also there is a 
slight improvement on the higher notes such as 
are occasionally reached by sopranos and violins. 
A certain vague sense of muffled sound has alto- 
gether disappeared. 

STAFF COMMENT 

THE experimenter writing the above experi- 
ence, Frank Wendell, of Los Angeles, has 
accomplished what is being done nightly in the 
large broadcasting stations, where the process of 
balancing the scale of frequencies is known as 
"equalization." With outside or "nemo" 
pickups, transmitted over landline to the broad- 
casting station, certain frequencies are trans- 
mitted with less fidelity than others, and the 
boosting up of the delinquent tones is accom- 
plished in much the same manner as our corres- 
pondent brought up his high notes. 

The average cone loud speaker in comparison 
with the average horn, is much better on the 
low notes. The same holds true of the resistance- 
coupled amplifier as compared with other am- 
plifying systems; but this type of amplifier also 
has a distinct cut-off on high frequencies. The 
combination, therefore, is one that favors the low 
frequencies often to such an extent that there 
exists the low-frequency rattle referred to. 

In the case under consideration, the high notes 
have been boosted by substituting a reactance 
in place of the resistance. It is probable that the 
response curve of the reproducing system has 
been leveled out a bit. That is, all frequencies 
reach the ear with a closer approach to their 
relative amplitudes or volumes. 

Taking out a coupling resistor and substituting 
a comparatively low inductance choke coil will 
always increase the amplification of the higher 
notes more than it increases the amplification of 
the low notes. The lower the inductance of the 
choke coil, the more will be the difference. There 
is no reason why the average broadcast fan 
should not improve reception by "equalizing" 
his receiver in this manner. A resistance-coupled 
amplifier (in any receiver) most easily lends itself 
to changes of this nature. 

VARYING THE AMOUNT OF EQUALIZATION 

AN ORDINARY amplifying transformer is 
probably the most readily available form 
of inductance or choke coil. The primary, in the 
case of the average transformer which may be 
on hand, should be used. 

The high notes will be brought up most if only 
the primary of the transformer is used. There will 
be less difference from straight resistance coup- 
ling if the secondary is used. Different degrees 
of equalization will be obtained if the primary 
and secondary are connected in series, with, first, 
the grid and plate posts strapped (using the B 
and F posts as terminals) and, secondly, with 
the grid and B posts strapped. 

The grid leak of the tube out- 
putting to the choke coil is not 
touched but the bias applied 
through the leak should be increased 
by about 4.5 volts. 



Connect speaker 
to set through 
o output device 



- A -B +C -9 -40 +180 



FIG. 5 



The Listener's Point of View 



LISTENERS GUESTS OR CUSTOMERS 



A 



SIR: 



I READER at Long Beach, California, 
addressed us not long ago as follows: 



May I be permitted to call to your attention 
the excellent and timely article appearing on 
page 1 5 of Radio News for July, 1927, entitled 
"The Fly in the Ointment," by one Nellie 
Barnard Parker? 

A great many listeners hereabouts were struck 
by the miserably poor taste displayed by the 
writers of the "can't-the-announcer-be-choked" 
and the "sprayed-with-petroleum" telegrams 
to which the writer refers; and one of us, at least, 
was equally impressed by the sportsmanship dis- 
played by the announcer in reading such tele- 
grams to us at all. 1 think that you will agree with 
the author of the article in question that '. . . 
when a company has spent thousands of dollars 
to broadcast a program, it has bought the right 
to let you know who your host is and what it 
has to sell.' 

I, for one, would like to see a similar stand 
taken by RADIO BROADCAST; and I believe that 
such a stand, in your columns, would more nearly 
present the average "Listener's Point of View" 
than does much that now appears there. 

G. I. RHODES. 

Here, indeed, was an invitation for your de- 
partment editor to adopt a policy and if there 
is anything an editor, of any variety, keeps an 
eagle eye out for, it is "policies." Policies are 
what enable him to get his stuff written. So we 
swam into the article, a most entertaining one. 

The specific fly in the ointment complained 
of was an incident in connection with the broad- 
casting of opera by KFI and KPO last season, as 
the indirect advertising donation of a certain 
petroleum corporation. 

The opera broadcast was unquestionably one 
of the outstanding musical treats af- 
forded West Coast listeners that sea- 
son. In the intervals between the acts 
the announcer read a number of 
telegrams of commendation and ex- 
plained, with some precision, just who 
was financing the broadcast. "And 
then," says the author of the article 
referred to, "right out of the sky, 
came the fly in the ointment! A man 
wired in: 'We are enjoying the pro- 
gram but can't the announcer be 
choked off and let us have opera with- 
out telegrams and advertising?" And 
pretty soon another 'guest' wired his 
objections against being 'sprayed 
with petroleum' while he listened. 
Clever, yes, but it struck one listener 
at least that when a company has 
spent thousands of dollars to broad- 
cast a program, it has bought the 
right to let you know who your host 
is and what it has to sell." 

That was the case in question. We 
are hardly fitted to pass on its merits 
since we didn't hear the broadcast. 
It is quite possible that the number 
of telegrams read and the amount 
of advertising dished out were en- 
tirely within the bounds of reason. 
In fact this seems probable if there 
were but two unfavorable com- 
ments on it. As the writer points 
out with some show of logic, the 



By John Wallace 

reading of a telegram of commendation sug- 
gests the sending of them to other listeners, 
and if a large number is received "they are per- 
manently bound and the next time there seems a 
possibility of interesting some firm in paying 
the fiddler for an expensive program, this bulky 
volume is brought forth." Thus the telegram 
reading may in some cases react finally to the 
listeners' benefit. 

But departing from this particular instance 
wherein the adverse criticism may not have been 
entirely warranted, the writer goes on to general- 
ize and takes the stand that adverse and de- 
structive criticism of a better-than-average 
program is never justifiable. This, it seems to us, 
is stretching the point to absurdity. She says: 

You are free to steer your airship where you 
please, casting out your line knowing that there 
are just as good tunes on the air as ever were 
caught. Such being the case, why send in thought- 
less messages to mar the perfect pleasure of your 
host? Let him sing his little solo without having 
the anvil chorus crab the act! 

It is only fair to say that those who criticise 
the big programs are in the minority, but there 
are just enough of them to destroy that fine 
edge of joy and what-a-good-boy-am-I feeling the 
sponsors and operators have. 

Every graduate operator of a radio is a super- 
critic of the air. Like an insect of the ether, the 
true radio bug goes sniffing through the air with 
his little feeler; when he "contacts" with some- 
thing he likes, he settles upon it with a pleasant 
little hum. But if it pleases him not, he is liable 
to plant a sting, if he is that kind of a bug. 
How much nicer it would be if he would remem- 
ber that the sponsors and announcers are just 
big boys trying to get along! They are not inocu- 
lated against praise. It takes on them beautifully 
and they break out with brighter and better 




THE SANKA AFTER DINNER COFFEE HOUR AT WEAF 

Heard over this station on Tuesday evenings at 7:30. They should re- 
ceive some kind of reward for getting the maximum number of words 
into the title. Anyhow, here are the performers 



programs. They invite and welcome constructive 
criticism and helpful suggestions, but mere 
"razzing" and discourtesy never fanned a gener- 
ous impulse into flame. Just be human, kindly 
and courteous, remembering that the announcer, 
like the fiddler, is doing the best he can. 
And don't be the fly in the ointment! 

We quote this writer at such length because 
hers is a point of view that is all too widely 
held, namely: that the purveyor of radio pro- 
grams is your host and that all the rules for 
polite drawing room conduct should operate 
in your attitude toward him. 

When a man invites you to his home for dinner 
he does so as a private individual, and however 
burnt the potatoes may be, it is not common 
politeness for you to throw them at him. But if 
the same man sets up 'a restaurant and you 
happen in there to eat, you are perfectly justi- 
fied in calling him all sorts of names if his chef 
has too highly seasoned the lobster tbermidor. 
He has removed himself from the role of private 
individual and become a purveyor to the public. 
He has become, to use the word loosely, an artist, 
and by universal assent any and all of the prod- 
ucts of the artist are open to criticism and he 
may not protest. By his very act of setting him- 
self up as an artist he tacitly agrees to submit to 
any opprobriums that the citizenry feels inclined 
to hurl at him. This is true of every sort of artist 
chef, singer, movie producer, poet, electric re- 
frigerator manufacturer, sculptor, street cleaner, 
painter or sponsor of broadcast programs. 

If a man wants to buy himself a box of paints 
and surreptitiously records on canvas his im- 
pression of the cherry tree in the back yard or 
sunset on the drainage canal no one has a right 
to comment on the way he does it. It is entirely 
his own affair as long as he keeps it 
his own affair by contenting himself 
with hanging the finished works on 
his own wall. But if he starts sending 
his pictures to the exhibition galleries 
he, by that gesture, professes himself 
to be an artist, and his work to be 
art; and he automatically becomes 
perfectly legitimate meat for anyone 
to pounce upon who cares to. 

If what he exhibits as art is inex- 
cusably bad, the good name of Art 
is threatened. And since Art is not 
his own private possession but is held 
by common consent to be in the cus- 
tody of the great unwashed public, 
it is incumbent upon that public to 
weed out with vituperatives anything 
that threatens to cast a smirch upon 
it. The commentary that the public 
makes is known as Criticism. Criti- 
cism may be of many kinds, favorable 
or unfavorable, constructive or de- 
structive, gentle or splenetic, com- 
petent or incompetent. The writer of 
the article discussed, and those of 
the same misguided frame of mind, 
would object to any criticism that 
does not fall into the category of 
favorable or constructive. This is ob- 
viously silly and results from a com- 
plete misconstruction of the function 
of criticism. Gentle-spirited senti- 
mentalists get all hot and bothered 



38 



RADIO BROADCAST 



NOVEMBER, 1927 



and are filled with great sympathetic aches when 
some public performer gets it in the neck from 
a sharp tongued critic. They decry the critic as 
mean and lacking in human qualities. But in the 
case of a genuine artist their sympathy is wasted. 
A true artist doesn't mind adverse criticism 
much; he is his own best judge of whether his 
work is good or bad. On the contrary he is 
rather stimulated by it. Splenetic or strongly 
biased criticism may be far more effective in 
egging him on to do better work than soporific 
boquets. The only criticism to which he is likely 
to object is the incompetent kind and of this 
there is, of course, plenty. 

The two critics of the KFI-KPO opera broad- 
cast may have been incompetent; they may not 
have been aware of all the facts, viz.: that a cer- 
tain amount of advertising was necessary if the 
broadcast was to pay for itself. As we have said, 
we did not hear the program and do not know 
whether this reading of telegrams was carried 
to excess or not. But not all criticism of radio 
programs by minority calamity howlers is in- 
competent. A great deal of it is very much to 
the point (including, of course, all our own sage 
pronunciamentos.) 

The fact that a majority of the listeners are 
perfectly satisfied with the way any given radio 
program is presented does not mean that any 
criticism on the part of a few of the minority 
is worthless. The oft-repeated phrase about 
giving the public what it wants is, at best, just a 
phrase. True, some effort is made in this direc- 
tion, but the public is not at all sure what it does 
want, seldom expresses itself on the subject, and 
finally, finds it the course of least resistance to 
take what it gets. 

The masses continue to be satisfied with what 
they are getting until something better comes 
along. Then they accept the improvement with 
the same placid satisfaction perhaps wonder 
why they were so easily pleased with the old 
but make not the slightest effort to secure further 
betterment. It is up to the minority kickers and 
mud slingers to secure for them these improve- 
ments. 

Your average radio listener was perfectly 
satisfied with broadcasting as it existed in 1923. 
His unimaginative and uncritical mind could 
conceive of nothing better. He was getting pro- 
grams made up largely of cheap jazz and cheaper 
talks. To live up to their views, the advocates 
of " throw-away-your-hammer-and-get-a-horn " 
would have to argue that things should have been 
left for him just as they were. He was satisfied; 
his cup of joy was full ; why attempt to overfill it? 




BOB CASON AND REBER BOULT 

Artists at station WLAC, pianist and baritone 
respectively. They call themselves the "Thrift 
Twins" for some reason not apparent in the 
photograph 



But what has happened since then? Programs 
have improved and his taste has improved with 
them. He has thrown away the cup and has 
graduated to the mug, which also is filled to the 
brim. Having a mug, will he now demand a 
schooner? He will not. 

The conclusion that we have been laboring, 
somewhat heavily, to reach, is that it is to the 
mud slingers and knockers, the minority critics 
or "Flies In the Ointment" that most of the 
credit is due for the rapid strides that radio has 
made. Back in radio's dark ages at least fifty 
per cent, of every station's time was devoted to 
unendurable tin pan jazz. The passive listeners 
stood for it. The knockers objected. It was elimin- 
ated and the passive listeners found themselves 
with fifty per cent, more entertainment for their 
money and all through no effort of their own. 

Radio has grown up considerably but it still 
has a few bad habits hanging over from its in- 
fancy. It is up to the knockers to knock these 
out. If radio is to be a Bigger and Better man 
than it was a boy it is up to the knockers to 
pummel it into this new shape. The soft soapers 
and dispensers of ointment can do no more for 
it than to make it a self satisfied mollycoddle. 
Let there be more flies in the ointment! 

The British Broadcasting Company 

Gets Razzed 

* 

WE ARE unable to give any very valu- 
able dissertation on broadcasting con- 
ditions in England, at this distance. 
But from what we read there seem to be con- 
tinual rumblings in the tight little isle, and most 
of them to the effect that the British Broadcast- 
ing Company is too highbrow. We have just re- 
ceived a copy of a thirty-eight page pamphlet 
by one Corbett-Smith flaying the administration 
of the B.B.C. A decidedly long-winded affair, it 
gets down to points occasionally: 

When one sets out to give a radio entertain- 
ment, whether music, poetry, drama, speech, 
"variety," or anything else, one visualizes (or 
should visualize) not the few who are already 
educated in some measure to appreciate the best 
in these various forms of art, but the vast many 
of our people to whom beauty has hitherto been 
a closed book the great mass of our folk who 
have never heard good music or noble poetry or 
any of our incomparable English literature and 
so who pretend impatiently to disdain these nice- 
ties of civilization, as they would call them. . . . 
Every single radio program should be so built aiitl 
presented as to form a perfect fusion of art, educa- 
tion and popular entertainment. 

The type of mind which is usually associated 
with scholastic education is hopelessly out of 
place in radio work. And there is another cause 
of the B. B. C.'s failure. It is the born showman 
of a very special quality that is needed. The man 
with the widest possible range of interests, with 
"an accute sense of the inter-relationship of every 
kind of activity." Radio entertainment demands 
not the depth of the scholar but the breadth of 
the sensitive man of the world. 

Showmanship, in varying degree, is needed for 
every single feature of radio entertainment. 
The "superior person" may sometimes scoff; 
but that person does not interest us. We have 
to compel and to rivet attention. We need, also, 
strong and vivid personality. The personality of 
the leader of men, not of a cold-blooded corpora- 
tion. And we need absolute sincerity, both of 
purpose and utterance. 

Now the B. B. C. have not begun to appreciate 
anything of this. Instead of making a Charles 
Dickens their director of programs they have 
put in a Matthew Arnold, the apostle of culture. 
Dickens enjoyed everybody and everything, even 
Fagin and Mr. Murdstone. That was the secret 
of his art and of his success. The B. B. C. seem 
to enjoy nothing, not even themselves. 

It is necessary to emphasize this total lack of 



sympathy with the people at large, because it 
strikes at the root of the matter. The B. B. C. 
are forever vaunting the intensely democratic 
character of their service when, in fact, it is about 
the most aristocratic business in the country. 
The House of Lords is an assembly of plebs 
beside it. 

Wherein, if Mr. Corbett-Smith's words are to 
be taken as true and he certainly sounds con- 
vincing we see that a government-controlled 
monopoly is not one of the best ways of providing 
satisfactory radio programs. The point that the 
writer pounds in throughout the length of his 
diatribe is one which, we think, is well worth 
making, namely: that radio's principal service is, 
after all, for the masses. The so-called intellectual 
class is not interested in radio at all. Its members 
do not own receiving sets nor would they listen 
to one if it were given them. This is not due 
merely to snobbishness; their time is otherwise 
occupied, and of other means of entertainment 
they have more at their hand than they can 
make use of. 

But we in the United States have no reason to 
fear such a state of affairs as Mr. Corbett-Smith 
complains of. Radio stations in this country are 
operated essentially for the masses. This is the 
natural result of a competitive system which de- 
pends for its reimbursement on advertising, di- 
rect or indirect. A maximum number of listeners 
must be the aim of every station which is not 
endowed or privately financed. In fact, here, a 
condition exactly the opposite of that alleged to 
exist in England is likely to obtain. A majority 
of stations, in their devotion to the masses, 
quite neglect the upper fringe of listeners. This 
is not true of the two score or so better stations. 
Careful and intelligent planning has enabled 
them to present programs appealing to the widest 
possible range of tastes. Their procedure is, first, 
to arrange a program that definitely appeals to 
the great mass of listeners, and secondly, to 
further manipulate it so as to effect a compromise 
with the upper crust of listeners. 

We, from viewing the subject too closely, are 
likely to forget how exceedingly well this has been 
done. Take, as an example, the Atwater Kent 
Hour. A straight appeal to the masses is made 
in the making up of these programs. While the 
selections are limited to the classics and to the 
opera, it is almost exclusively the sure-fire hits 
and tried and true tunes that finally find their 
way on to the program. But while the highbrow 
may think some of the tunes are banal and over- 
worked, they've got him on another score: he 
cannot afford to ignore the importance and artis- 
try of the performers Atwater Kent employs to 
put them over. 




ANITA DEWITTE HALL OF KO1L 
She is the versatile program director, organist, 
pianist, and "Mother Hubbard" of the staff 



The R. G. S. "Octamonic" Circuit 



How Laboratory Discoveries Were Moulded to Produce the Commercial 
Design of a Sensitive and Selective Set Details of a Striking 1928 Development 



THE first article in thisseries(RADio BROAD- 
CAST for October) described the concep- 
tion and theory of the fundamental 
"Octamonic" principle, which obtains a high 
degree of selectivity by a function of the vacuum 
tube rather than by any special circuit contrap- 
tions. It was shown that the super-selectivity 
did not impair the tone quality as is the experi- 
ence in tuned radio-frequency circuits. The high 
frequency of the second harmonic current per- 
mits a very sharp resonance curve without un- 
duly compromising the side band amplification 
which is absolutely necessary for the proper 
reproduction of the high-frequency audio tones. 
Other points of invention were also discussed, 
but it is a long road from invention to commer- 
cial design. It is one thing to build a laboratory 
model which proves the principle of an idea and 
quite another thing to plan the construction of 
a radio receiver which will meet all of the com- 
mercial conditions encountered in the field with- 
out a great many operating controls. 

The purpose of this article is to reveal the de- 
sign and constructional information which have 
been found necessary. These data have been ac- 
quired only after a great amount of original 
investigations, for there appeared to be little or 
no information available on the subject of second 
harmonic generation, tuning, amplification, and 
detection. The subjects will be discussed in the 
order in which they occur in our laboratory note- 
book. While the order may appear to be unusual, 
the facts were accumulated in just that sequence. 
The first study was confined to the harmonic 
generating tube. The proper operation of this 
tube insures the success of the entire receiver. 
The first article showed a C potential bias on the 
grid of the harmonic generator this bias causing 
the tube to operate on the lower knee of the grid 
voltage-plate current characteristics. This point 
of the characteristic gives the greatest amount 
of second harmonic energy as the unequal am- 
plification between the two halves of the carrier 
wave is greatest at this point. However, with the 
standard commercial types of vacuum tubes 
operating on standard units of B potential such 
as 22 volts, 45 volts, or 90 volts, the amounts of 
negative C bias required for harmonic generation 
do not correspond with the commercial units of 
C potential available with the standard C bat- 
tery. For instance, the maximum amount of 
second harmonic energy appeared to be gener- 
ated by a standard CX-JOI-A tube operating on 
45 volts plate potential with about 2 volts minus 
grid potential. Such a C bias cannot be obtained 
conveniently from dry batteries. 

Of course, the easiest way to obtain a 2-volt 
negative bias on the grid of the harmonic generat- 
ing tube is to utilize the principle of an IR drop. 
By running the filament return of the tube 
through a fixed 6-ohm resistance, a 2-volt drop 
may be obtained and if this fixed resistance is 
placed on the negative filament lead a negative 
2-volt bias is available for the grid. Fortunately 
the operation of the second harmonic tube was 
not affected by running its filament on 4 volts, 
the remaining A battery potential available for 
the filament after 2 volts had been extracted 
by the fixed resistance for the grid bias. In fact, 



By DAVID GRIMES 

it was found that the filament of the harmonic 
tube could be run much lower than this without 
in any way impairing its second harmonic 
generating properties. This is explained graphic- 
ally by Fig. i which shows the grid voltage-plate 
current characteristic of a vacuum tube which 
is operated at various filament voltages. The 
various filament temperatures materially affect 
the upper portions of the characteristic but have 




FIG. 



little or no effect on the lower knee of the curve. 
The filament voltages only affect the saturation 
point of the tube. 

In the vernacular, this is a fortunate "break" 
in design work as it affords a very simple arrange- 
ment for the harmonic generator which is very 
stable in its performance and exceedingly inex- 
pensive. As a matter of fact, a series of tests 
shows that the filament voltage of the tube 



could be cut down as low as 25 volts before the 
second harmonic currents were affected, and the 
C bias could vary from i \ to 2 volts. This more 
than covers the variation in A battery potential 
during the period between full charge and dis- 
charge of the A battery. The 45 volt B battery 
on the harmonic generator was also found to 
be a non-critical factor. Fairly large amounts of 
second harmonic currents were generated by this 
tube when the voltage had dropped as low as 34 
volts or was raised as high as 50 volts. 

PROBLEMS IN THE HARMONIC GENERATOR 

EXCESSIVE B potentials on the harmonic 
generator created an unusual and peculiar 
difficulty. There existed a tendency toward 
oscillation on the short wavelengths of the input 
tuning condenser to this harmonic generator 
when the plate voltage was boosted too high. 
The source of this oscillation is not obvious and 
evaded detection for some little time. One is ac- 
customed to expect oscillation in a tube only 
when there is a deliberate external feed back 
circuit or through the internal electrode capaci- 
ties only when the plate circuit is tuned to the 
same frequency as the grid circuit such as oc- 
curs in a tuned radio-frequency system. As seen 
in Fig. 2, the plate circuit of the harmonic genera- 
tor is tuned an octave higher in frequency than 
the grid circuit and under these conditions the 
well known ordinary oscillation cannot occur. 
As a matter of fact the primary of the second 
harmonic transformer possesses considerable 
effective inductance as the result of the tuning 
to the higher octave. The number of turns in 
the harmonic transformer primary alone is in- 
sufficient to cause oscillation in the harmonic 
tube unless the secondary is tuned to the higher 
octave. When this is done, there is an increase in 
effective inductance over and above the actual 
inductance which causes the oscillatory difficul- 
ties mentioned, with excessive plate voltages on 
the harmonic tube. 

The remedy for the difficulty outlined above 



L 
105 




/ CX 301-A 
/Harmonic Generator 



Common Rotors 

y. 0.00025 mfd. / 
4 II-*-' -/ 






^\ 

', B 
Tuned to 
2F 


in ^> ^ 


^ 


2 rr.ej 




< 
< 
< 

1 




.001 



To Audio 
Amplitier 



1 , 

II 


1 


1 


1 








45V. 



FIG. 2 



40 



lies in reducing the number of primary turns in 
the harmonic transformer to such a point that 
the effective inductance at the highest com- 
mercial voltage will not produce the oscillation 
described at the short broadcast wavelengths. 
Fig. 3 shows the design details of the tuned 
harmonic transformer used for connecting the 
output of the harmonic generator to the input of 
the detector tube. It will be noted that the 
secondary of this transformer has been made 
unusually small much smaller than would be 
expected for merely tuning the double frequency 
involved. Commercial considerations have con- 
trolled the design of this transformer as well. 
The general tendency in the modern design of 
the radio receiver is to combine as many of 
the tuning condensers as possible on one shaft 
exercising the proper care in the balancing of 
the condensers and coils so that they will tune 
alike for all the broadcast wavelengths. In the 
R. G. S. "Octamonic" design, it seemed desir- 
able to combine the tuning condenser on the 
secondary of the harmonic transformer with the 
tuning condenser on the input to the harmonic 
generator. The problem is not as simple as the 
combining of condensers controlling similar 
circuits. The harmonic condenser must always 
tune to half the wavelength of the fundamental 
tuning condenser in the input of the harmonic 
generator. Furthermore, another limitation is 
imposed because all available gang condensers 
have been designed for tuned radio-frequency 
circuits and have therefore equal capacity in all 
the individual members of the gang. 

This means that the second harmonic trans- 
former must be so designed that a standard 
o.ooo35-mfd. tuning condenser must tune the 
half wavelength band from 100 to 275 meters at 
exactly the same settings on the dial as a similar 
condenser tunes the fundamental coil for the 
respective corresponding fundamental wave be- 
tween the 200 and 550 meter broadcast band. 
A consideration tuning formula shows that this 
can easily be accomplished if the inductance 
of the secondary of the harmonic transformer is 
made exactly equal to j of the inductance of the 
fundamental tuned secondary on the input to 
the harmonic generator tube. 

SOURCES OF SELECTIVITY 

ANOTHER fortunate "break" aids in the 
ganging of these two condensers, as one of 
them is extremely sharp in tuning while the other 
is relatively broad. The real selectivity of the 
receiver is obtained by the tuning condenser on 
the input to the harmonic generator as the 
harmonic currents generated in this tube are 
proportional to the square of the resonant input 
carrier voltages resulting from this tuning con- 
denser. The tuning condenser across the second- 
ary of the harmonic transformer is no sharper 
than the ordinary tuning circuit on the input to 
a detector tube. Slight variations are therefore 
permissible in the coils and condensers without 
jeopardizing the performance of the receiver. 







RADIO BROADCAST 




@K 



-- 41 threads 
Coil D rf-.li wo""d with 

2 Required f * *1 No.30 

-#&* tr~1 enameled 
" I wire 




TYPICAL ASSEMBLY OF COILS 

FIG. 3 

The two gang condensers may have the same 
grounded rotor shaft as there is no need for any 
special insulating between these circuits. It is 
true that there are different grid biases on the 
two tubes to be tuned, but the positive bias on 
the grid of the detector tube may be supplied 
by the grid leak connecting from the plus fila- 
ment of the detector tube directly to the grid, 
while the negative C bias on the harmonic gen- 
erator is supplied through the common rotor and 
the secondary of the fundamental transformer 
in the grid circuit of the harmonic generator. 
The blocking condenser in the grid circuit of 
the detector effectively separates the positive 
potential on the grid of the detector and the 
negative C bias which exists in the rest of the 
harmonic secondary by virtue of the common 
grounded rotor shaft. As the negative potential 
is obtained by a resistance drop, as previously 
described, it is obvious that both the high-fre- 
quency currents in the detector grid circuit and 
the broadcast frequency currents in the harmonic 
grid circuit must return to their respective fila- 
ments through this resistance. Feed-back diffi- 
culties and oscillation would absolutely occur at 
this point in a tuned radio-frequency system, 
but no difficulties are encountered in the R. G. S. 
"Octamonic" because these two carrier currents 
are of different frequency and cannot, therefore, 
interfere with one another. 

One thing should be made very clear at this 
point of the discussion. There is a fundamental 
difference between detection as such, and the 
generation of second harmonics. As discussed in 
the first article of the series the operation of a 
tube on the knee of its characteristic curve 
will produce not only second harmonic but 



/, 



Time 

HARMONICfGENERATOR STAGE 




'Decrease due 
to rectification 



DETECTOHj STAGE 



FIG. 4 



NOVEMBER, 1927 

audio currents as well. In this circuit the tube 
is acting not only as a harmonic generator 
but, incidentally, as a detector. No method is 
known at present for the efficient generation of 
second harmonics without the incidental detector 
action occurring simultaneously. However, in the 
detector stage, two possibilities are present. 
Either the grid leak system of detection or the 
C battery system of detection may be used. 
The grid leak system is slightly more sensitive 
on very weak signals while the C battery system 
will deliver more audio energy on local reception 
without distortion. A study of these two types 
reveals some interesting facts. There is present, 
along with the detector action, some incidental 
generation of second harmonics, when the C 
battery detector is employed. This would be 
expected from the considerations already dis- 
cussed in connection with the harmonic genera- 
tor. However, second harmonic currents are 
almost wholly absent in a detector tube employ- 
ing the grid leak system. This means, that 
detector action cannot be confused with harmonic 
generation. They may or may not occur simul- 
taneously. The grid leak detector simply cannot 
be used in the generator stage for the creation 
of second harmonics. The harmonic generator is 
not a detector. 

WHAT TYPE OF DETECTOR CIRCUIT? 

IT NOW remains to determine which type of 
circuit should be used in the detector stage. 
Both the C battery and grid leak circuits were 
subjected to an extensive series of tests. The grid 
leak system was found to be much more satis- 
factory and much more stable. The tone quality 
was not impaired by the grid leak system and the 
distortion which occurred on local reception 
when using the C battery system, entirely dis- 
appeared when the grid leak system was sub- 
stituted. The results were so consistently con- 
trary to those anticipated that considerable data 
was gathered in an effort to explain the cause. 
Fig. 4 shows graphically just what occurred and 
why it is desirable to employ the grid leak system 
in the bona fide detector. It will be noted that the 
incidental detection occurring in the plate cir- 
cuit of the harmonic generator is represented by 
an increase in the plate current the increase 
being proportional to the modulation on the 
incoming carrier waves. Quite the reverse takes 
place in the detector circuit. Here the plate cur- 
rent decreases upon detection due to the choking 
action of the grid leak and condenser in the grid 
circuit. The decrease in plate current is propor- 
tional to the modulation on the incoming carrier 
waves. The rectified or audio currents existing 
in the plate of the harmonic generator are not 
utilized but, in turn, flow through the B battery 
circuit. The detected or audio currents in the 
plate circuit of the detector go through the 
primary of the first audio transformer and then 
flow through the B battery circuit. With these 
two audio currents opposing each other in the 
B battery at all times there is no audio voltage 
drop occurring therein. If a C-battery detector 
were employed the two audio currents would in- 
crease and decrease simultaneously, causing 
excessive audio voltage drops in the common B 
battery. 

As brought out in the previous article, the 
R. G. S. "Octamonic" receiver obtains its 
super-selectivity through the sacrifice of some 
of the radio-frequency energy. But as radio- 
frequency energy is very easily obtained by any 
number of r.f. amplifying circuits and selectivity 
is not so easily obtained, the sacrifice is well worth 
while. However, some form of r.f. amplification 
must be placed ahead of the "selectivity" circuits 
just discussed. Various r.f. arrangements have 
been investigated and the one shown in Fig. 5 is 



NOVEMBER, 1927 



THE R. G. S. "OCTAMONIC" CIRCUIT 



41 



recommended. This shows one stage 
of radio-frequency amplification 
only as one stage has been found to 
be more than ample for operating 
the harmonic generator on even the 
most distant stations. The antenna 
is very closely coupled to a tuning 
circuit which serves mainly to bring 
the antenna circuit to resonance at 
the frequency desired. The carrier 
wave is then amplified and applied 
to the harmonic generator through 
a special equalizing coupling circuit 
which is designed to pass all of the 
broadcast frequencies with approx- 
imately undiminished amplitude on 
to the harmonic generator. The 
theory of the operation of this un- 
usual coupling is rather simple. The 
total winding consists of 21 turns 
which is the proper primary for the 
longest wavelength of 550 meters. 
Then a tap is taken off at 7 turns 
which is approximately the proper 
primary for the shortest wavelength of 200 me- 
ters. A o.ooo25-mfd. fixed condenser is connected 
between the tap and the filament of this amplify- 
ing or coupling tube. A variable non-inductive 
25O-ohm equalizing resistance is placed in series 
with the total winding. The short waves pass 
readily through the fixed condenser to the fila- 
ment while the longer waves tend to pass more 
and more through the entire winding because of 
the increasing reactance of the fixed condenser 
to the lower frequencies of the longer waves. 

This first amplifying tube has been designated 
a coupling tube since its main function is purely 
a coupling and amplifying action rather than 
any aid to the tuning. The coupling to the an- 
tenna is made as close as possible so as to derive 
the maximum amount of energy therefrom 
throughout the broadcast band. Such close 
coupling makes the tuning very broad and non- 
critical the real super-selectivity of the receiver 
being created by the tuning condenser on the 
input to the harmonic generator. In actual opera- 
tion, this antenna condenser appears to be 
sharper in its tuning than it really is because, 
after all, it has an indirect effect, though broad, 
on the amount of energy being transformed into 
second harmonic currents by the generating 
tube. This action gives it an apparent sharpness 
greater than that which is really occurring in 
the antenna circuit. 

CURIOUS MODULATION EFFECTS 

ONE very important factor in the design of 
the coupling tube circuit is modulation. 
Great care must be exercised in the design of this 
circuit to avoid any possibility of rectification 
action even on the louder signals. Otherwise, 
the extreme selectivity of the harmonic generator 
will be somewhat modified by a cross-talk or 




FIG. 5 

modulating action between a near-by high- 
powered local station and a distant station 
operating on an adjacent carrier channel. The 
action is as follows: The receiver in New York 
City is tuned to a weak station such as woo in 
Philadelphia operating on 508 meters. It is 
found that several dial degrees of silence are 
obtained between this Philadelphia station and 
WEAF, New York City, operating on 492 meters. 
However, WEAF is coming in with considerable 
field strength impressing considerable 492 meter 
energy on the grid of the coupling tube along 
with the energy from the Philadelphia station. 
If any rectification occurs on the strong signals 
from WEAF, audio currents will be set up in the 
plate circuit of this radio coupling tube which 
correspond to the program being sent out by 
WEAF. It must be remembered here that the first 
circuit is broad its function being amplification 



"^High External 
Resistance 





GRID VOLTS 



FIG. 6 



and not tuning. As a result, more 
WEAF energy may be present than 
the energy coming from Philadelphia 
even though the antenna tuning con- 
denser has been set in favor of the 
Philadelphia station. 

Now, the audio currents occurring 
in the plate circuit of the coupling 
tube as a result of the rectification 
of the WEAF carrier wave, will cause 
a plate voltage variation in this tube 
which corresponds to the program 
on the carrier wave of WEAF. This 
action will, in turn, affect and vary 
the amplification of any other carrier 
wave coming through the tube at the 
time, such as the Philadelphia sta- 
tion which is desired. The audio 
modulation or WEAF'S program will 
then impress itself on the carrier 
wave of the Philadelphia station in 
the same manner that the original 
audio currents at the studio of 
WEAF impressed themselves on the 
original carrier wave being sent out from WEAF 
on 492 meters. The result is that, while several 
dial degrees of silence are obtained between 
WEAF and woo, as soon as the Philadelphia 
station is tuned-in, the program from WEAF is 
found also to exist thereon in the form of cross- 
talk or cross-modulation. 

The remedy is to operate the coupling tube 
on the straightest portion of the grid-voltage 
plate-current characteristic curve. For the 
standard cx-3oi-A tube, this requires 90 volts 
on the plate and 42 volts negative bias on the 
grid. This point is very essential. In addition, it 
is desirable to have the maximum of coupling 
to the harmonic generating tube, not only from 
the standpoint of energy transfer, but also for 
the purpose of obtaining a fairly high effective 
resistance in the plate circuit of the coupling 
tube at the particular frequency for which the 
input to the harmonic generating tube is tuned. 
It is a well known fact that the resistance of a 
primary winding increases considerably at the 
resonant frequency of the secondary. At the 
same time the reactance passes through zero, of 
course. The closer the coupling the greater is 
the effective resistance of the plate circuit and 
resistance in the plate circuit tends to flatten 
out the characteristic curve of the coupling tube. 
This is shown in Fig. 6. This flattening of the 
characteristic curve still further reduces any 
tendency toward rectification in the coupling 
tube. 

A detailed discussion on the audio ampli- 
fier as well as a full explanation of the theory and 
operation of the harmonic wave-trap shown in 
the antenna circuit will be taken up in the next 
article of the series. The next article will also 
describe in further detail the best wiring arrange- 
ments. 



The 




Better Control of Oscillation Is a Feature of This New Receiver 
The Story of Some of the Difficulties Surmounted in Its Design 



ANY radio engineer can make a single re- 
/-\ ceiver work in the laboratory but when a 
^- factory turns out five hundred a day, 
each of which must be thoroughly tested, the 
problem becomes somewhat more complex. It 
becomes one not only of manufacturing small 
mechanical parts to a high degree of precision and 
of simplified assembly so that mistakes are diffi- 
cult to make, but one of following a circuit that 
is electrically sound and as foolproof as possible. 

Circuits that are highly sensitive are often 
highly critical in their adjustment, necessitating 
that they pass through the hands of a well 
trained tester before they can be released. What 
every set manufacturer wants is a receiver de- 
sign such that manufacturing costs and assembly 
problems are reduced to the bone, that testing 
methods are neither complicated nor expensive in 
point of time, and that adjustments are few. 
Simplicity of design is not the controlling factor, 
for the simplest circuit must embody the same 
trouble producing elements as the most complex. 
For example, every engineer knows that induc- 
tance in the plate circuit of a radio-frequency 
amplifier is necessary to transfer energy from one 
circuit to the following tube; but he knows too 
well that including this inductance tends to 
make the previous tube oscillate. One method of 
preventing oscillation is to feed back to the input 
circuit some of the energy that appears in the 
output circuit in such magnitude and phase that 
the tube is no longer unstable. Owing to the 
fact that unity coupling is necessary to obtain 
complete prevention of oscillation (neutraliza- 
tion) at all frequencies, it is impossible to neu- 
tralize the amplifier over more than a narrow 
band at one time. Often the circuits are balanced 
at the shortest wavelengths, for the tendency to 
oscillate is greatest there; but this is apt to result 
in poor transfer of energy on the longer waves. 

If it were possible to neutralize a receiver com- 
pletely throughout its tuning range and to in- 
clude sufficient primary inductance with close 
enough coupling to the secondary to produce 
proper amplification on the longer waves, the 
design engineer's problem would be simple. Un- 
fortunately, in spite of the neutralization process, 
it is often impossible to utilize the utmost desira- 
ble amount of primary inductance and coupling, 
and the longer waves suffer. 

A method that has been used to maintain the 
circuits in a two-or three-stage radio-frequency 
amplifier free from oscillations is that of including 



By J. O. MESA 

resistances in the grid circuits of the amplifying 
tubes. It was found in the Freshman laboratories 
that, with sufficiently large primary coils, the 
resistances became rather large, of the order of 
500 ohms. This method of "holding down" an 
amplifier is shown in Fig. I, and in Fig. 2 is the 
equivalent circuit. 

Mathematics will show that for every resist- 
ance, another, smaller in actual value, can be sub- 
stituted, as in Fig. 2, in the tuned circuit itself 
to accomplish the same end, namely, cessation of 
troublesome oscillations. In fact, when such ex- 
ternal resistances are used, the selectivity of the 
circuit suffers, and at the same time the ampli- 
fication falls off, showing conclusively that this 
external resistance has in effect added considera- 
ble damping to the tuned circuit itself. 

There is a very serious objection to the use of 




FIG. I 



FIG. 2 



FIG. 3. 



resistances as in Fig. i. Under the usual condi- 
tions obtaining in a high-amplification circuit, 
the value of the stabilizing resistance is somewhat 
critical. If the correct value is exceeded, the over- 
all voltage gain of the radio-frequency amplifier 
is considerably reduced, while if the resistance is 
too small, the circuit oscillates violently. Further- 
more, any slight variations in the component 
parts which make up the radio-frequency ampli- 
fier change the value of resistances needed for 
best operation. 

The solution, naturally, lies in very close 
manufacturing limits on the values of inductance, 
capacity, and resistance, and for some time re- 
ceivers employing the resistance arrangement of 
Fig. I were built in the Freshman plant. In spite 
of the fact that the resistances were held accurate 
to within plus or minus i .25 per cent., difficulty 
occurred from oscillation or poor selectivity and 
lack of amplification too frequently for comfort. 
It became necessary to develop another stabliz- 
ing system. 

The new method of overcoming oscillations 
without the disadvantages previously mentioned 
was found by Mr. W. L. Dunn, Jr., and was 
developed by the engineers of the Freshman 
laboratory. This method is based on a principle 
which has been used for a long time in telephone 
equalizing circuits, and has been discussed 
mathematically by K. S. Johnson in his Trans- 
mission Circuits for Telephonic Communication 
and by Morecroft on page 92 of the new edition 
of his well known Principles of Radio Communi- 
cation. 

The circuit which has been utilized is shown in 
Fig. 3, and it may be seen to consist of a coil and 
condenser in parallel with a resistance in each 
branch of the parallel circuit. If the resistances 
in the two paths are equal to each other and 



equal to the square root of the inductance divided 
by the capacity, or: 

RL = Re = i/L/C 

the impedance of the circuit looked at from the 
standpoint of the previous tube is a pure re- 
sistance at all frequencies. 

Therefore, the plate circuit of the previous 
amplifier has no inductive reactance in it and 
so the tube cannot oscillate, provided the 
values of inductance, capacity, and resistance are 
properly adjusted. 

Limiting the magnetic feed back in the circuit 
by using small diameter coils and placing them 
at right angles to each other, and by using proper 
bypass condensers across impedances which are 
common to more than one stage, naturally aid 
in keeping the amplifier performing its required 
tasks. 

I he method of applying this interesting case 
of parallel resonance is shown in Fig. 4. Owing 
to the fact that some resistance is reflected into 
the circuit when a secondary coil is coupled to it 
and is tuned to resonance, the actual values of 
resistance used are different, 380 ohms being 
used in the condenser, or plate branch, and 350 
ohms in the inductance branch. The capacity 
used is about 100 micro-microfarads and is of the 
fixed-variable type, that is, a fixed condenser 
having attached to it a small variable capacity 
which may be adjusted in the factory so that 
the receiver does not oscillate. 

When it is realized that closer coupling and 
greater primary inductance may be used when 
such a circuit is employed, the gain over the 
grid resistance method of stabilization is evident. 
Nearly double the coefficient of coupling may be 
used between primary and secondary in this new 
system. 

THE RECEIVER 

TH E schematic diagram of a battery operated 
receiver using this principle is shown in Fig. 
5. This receiver is now being manufactured with 
large quantity production methods. It has 
been found that it is not subject to the difficulties 
encountered in the case of the grid resistances 
method of preventing oscillation. The condenser 
in the plate circuit of the radio-frequency tubes 
consists of curved spring plates with mica di- 
electric which can be flattened by means of a 
screw which is accessible to the inside of the 
cabinet. This condenser is adjusted at the factory 



JJy 

H==s^ 


= c 


:oo 

mmf. 




ti 


380u 
^\A^ 

1 




FIG. 4. 



NOVEMBER, 1927 



THE "EQUAPHASE" 



UX-201-A 



UX.201.A 



UX-200-A 



UX201-A 




Ant. 1 Ant 2 



C-40 



A- A* B45 
Rnd. 



B90 



B-l0 



FIG. 3 



so that the amplifier does not oscillate and does 
not require readjustment thereafter so long as 
tubes having the same plate impedance are 
used in the radio-frequency amplifier. When a.c. 
tubes are used a smaller capacity is needed owing 
to the high low impedance of these tubes com- 
pared with the average d.c. tube. 

The radio-frequency transformers have sec- 
ondaries which are wound on a small bakelite 
tubing and have individual turns 
slightly spaced. It has been found that 
this type of winding can be controlled 
so that the inductance of the coil 
may be held to within about 0.5 per 
cent, of accuracy when manufactured 
in large quantities. The primary of the 
radio-frequency transformer is a spiral 
wound on a wooden form, and is placed 
at the ground end of the secondary, 
thus having the advantage of a com- 
paratively large coupling and at the 
same time small capacity between the 
primary and secondary. 

The audio transformers are 
mounted on the tube shelf and have a 
4 to i turn ratio. The secondary wind- 
ings are of the split or balanced type 
which have very low distributed capacity and 
very low capacity between windings, with the 
result that a quite uniform amplification is ob- 
tained between 100 and 5000 cycles per second. 

The radio-frequency inductances and audio- 
frequency transformers as well as all the other 
apparatus which is not accessible to the controls 
on the front panel, are mounted on a spring sus- 
pended metal shelf. This shelf carries the tubes 
and is provided with rubber dampers so that 
there is no microphonic feed back. 



R.C.A. 
AiC.Tube 
UX226 



The variable condensers used are selected so 
that their capacities are equal to within 0.25 per 
cent, at two points. Since the plates are of heavy 
construction and have rather wide_ spacing, the 
capacities of the condensers in any receiver are 
practically identical throughout their entire 
range. The arrangement of the front panel of 
the "Fquaphase" may be seen in the photograph 
of this receiver which appears on page twenty. 

AUDIO FREQUENCY CHARACTERISTIC 
Device Tested : Transformer ES 2774 
Circuit Data : E A 5.0, E B 90, E c 4.5 




16 



FREQUENCY CYCLES PER SECOND 
Scale .95"per Octave 

INTERESTING CURVES 
Showing the characteristics of the audio 
transformers used in the "Equaphase" 

The volume control of the battery operated re- 
ceivers is obtained by means of a rheostat in 
series with the filaments of the radio-frequency 
tubes. This method has been used for several 
years on Freshman Masterpiece receivers and 
has left nothing to be desired. 

As mentioned before, a slight modification of 



43 



the constants of the elements used in the plate 
circuit of the radio-frequency amplifiers is neces- 
sary toadapt the circuit to the use of thealternat- 
ing current tubes of the ux-226 (cx-}26) type. 
Since the circuit does not oscillate and has high 
amplification throughout the broadcast range, 
the volume control can be obtained by means of 
a potentiometer across the secondary of the 
first audio-frequency transformer. This potentio- 
meter has the so-called logarithmic scale, that is, 
its resistance varies so that equal angular incre- 
ments on the control produce equal increments 
of volume. A schematic diagram of the house 
current operated "Equaphase" receiver and its 
power supply is shown in Fig. 6. The plate supply 
is of the conventional type using a ux-28o full- 
wave rectifier tube and having a two-section 
filter. Various plate voltages are obtained from 
taps on a resistor connected across the output of 
the filter. The grid bias for the various tubes is 
obtained from the drop across the resistance in 
the plate circuit of the tubes. 

Two independent tests are made on the sensi- 
tivity of each receiver before it is packed. These 
tests are made by two men who chyk each 
other's work without either knowing the other's. 
Around the laboratory is fed a continuous 1000- 
cycle tone of a certain amplitude which is main- 
tained constant. This is available at 
each test bench, and is used to modu- 
late a small radio-frequency oscillator. 
A very small part of this energy is 
picked up on a dummy antenna 
whence it goes through the receiver 
just as a radio signal would. The test 
man listens to it comparing it with 
the standard input looo-cycle tone by 
means of an attenuation box which is 
placed in the receiver output. In this 
way he reads the relative amplifica- 
tion of the receivers, and after fixing 
a certain standard he can reject any 
which fall below the required limit. 
Phonograph music is also fed around 
the test benches so that the test man 
can listen to music as well as his 
standard looo-cycle signal. 

Any slight error in a component part is dis- 
covered in this way before the receiver leaves 
the factory, in which case it can be sent back to 
the repair bench for final adjustment. 

It can easily be appreciated that this method 
of preventing oscillation is one which does not 
affect the selectivity of the receiver once it is 
properly adjusted. The selectivity of the " Equa- 
phase" is quite satisfactory enough for con- 
gested districts. 




FIG. 6 




By JOHN E. McCLURE 



"TTT IS seldom that a radio receiver design, or 

I kit, outlives a single season's popularity, and 

when the exception comes along, it gives 

assurance that it must be an unusually fine set. 

Such is the "Shielded Six." During this last 

year certain refinements of design have been 

developed, and the new improved model is now 

ready for the 1927-28 season. 

Mechanically, the design of the receiver is one 
of the prettiest of kit jobs, and the "Shielded 
Six" looks more like a carefully worked-out 
assembly for quantity production in a modern 
factory than a kit receiver. The whole set builds 
up progressively on a die-formed and pierced 
steel chassis, which is a radical departure from 
the often makeshift packing-case baseboards to 
which the home constructor is accustomed. The 
panel also is of metal, bronze, attractively decor- 
ated in the fashion of the new expensive factory- 
built sets, being utilized for this purpose. 

Electrically, the circuit design involves three 
stages of tuned radio-frequency amplification 
with controlled regeneration, a grid-biased detec- 
tor tube, and two stages of transformer-coupled 
audio-frequency amplification. In these respects 
the improved model is very like the original, and 
the only really startling improvements found in 
the set are circuit changes resulting in greatly 
increased selectivity, and the addition of vernier 
tuning dials found necessary because of the 
greatly increased sharpness of tuning. 



The antenna stage, or first radio-frequency 
amplifier, is left unshielded in the new model to 
increase the coil pick-up to a point where the 
receiver may be operated in apartment houses 
with no antenna at all, and yet give adequate 
loud speaker volume on powerful local stations. 
If the second, third, or fourth coils were un- 
shielded, selectivity would be affected, for 
energy pick-up on these coils would affect the 
selective tuning action of the tuned circuits. 
Shielding not only prevents pick-up of external 
interference, but possibly more important, en- 
tirely prevents extraneous interstage coupling. 

Losses in the r.f. circuits have been reduced 
to a minimum through the use of quite low 
resistance inductances, wound on threaded ribs 
of bakelite coil forms in such a fashion that they 
are practically air-supported. These inductances 
are tuned by means of newly designed, very 
rugged, condensers providing a semi-straight- 
frequency, straight-wavelength tuning curve 
which gives most satisfactory spacing of stations 
over the tuning dial scales. The set may be 
adapted for loop reception without a single change 
except to pull out the antenna coil and clip on 
two loop leads to coil socket posts 3 and 6. 
The new set seems amply selective for present 
broadcasting conditions, for, in Chicago, it will 
cut through a mass of thirty local stations and 
bring in out-of-town stations. 

While four tuned circuits are employed, only 



two tuning controls are used, this being made 
possible through extremely accurate matching 
of condensers and coils. All coils for a set are 
matched to within a quarter of one per cent, and 
the condensers are all checked and held within 
one per cent, of each other. Since the tuning of 
the three right-hand circuits is substantially 
identical, a mechanical link serves to turn all 
three condensers as the right-hand dial is turned. 
The antenna stage condenser is tuned separately. 

The audio-frequency amplifier has a highly 
desirable characteristic in that it amplifies prac- 
tically uniformly all frequencies between 30 and 
5000 cycles, above which frequency there is prac- 
tically no amplification. The highest funda- 
mental note of any musical instrument is 4192 
cycles and the jooo-cycle upper limit allows 
plenty of leeway for the handling of the highest 
fundamental frequency in music, and it has been 
proved that frequencies above 5000 cycles do not 
contribute, in any measure, to fidelity of repro- 
duction. Thus the interference caused by heter- 
odyne squeals developed between transmitting 
stations, by atmospheric noise and by the tube 
and battery noises, all of which are generally 
above 5000 cycles, are almost entirely absent. 

A group of people listening to the improved 
"Shielded Six" receiver operating in conjunction 
with a good cone loud speaker and receiving an 
organ program, will actually feel the vibration 
of the room in which the receiver is located, as 




O-CAmp. 
0-CDet 



THE CIRCUIT DIAGRAM OF THE IMPROVED SHIELDED SIX RECEIVER 



THE IMPROVED "SHIELDED SIX" 



45 




The parts needed for the Improved Model are 
listed below. They total exactly $95.00. While 
this price may seem a bit high in that fifty- 
dollar six-tube sets, completely constructed, are 
available, it must be remembered that the 
"Shielded Six" has been designed with unusual 
care and that all the parts have been very care- 
fully matched to insure satisfactory operation. 



PREPARATORY TO PLACING THE STAGE SHIELDS IN POSITION 
The arrangement of the Silver-Marshall triple link motion is distinctly shown in this pho- 
tograph. The transformers are, from left to right, output, second audio, and first audio 



they would were they in the original building in 
which the organ itself was located. 

A. C. OPERATION 

AC. OPERATION is so ridiculously simple 
with the "Shielded Six" as to require little 
description and if Sovereign or equivalent heater 
tubes are used, lighted from a filament trans- 
former, only minor changes need be made in the 
wiring. The standard Sovereign tubes have the 
heater leads coming out on top and all tubes 
should have their heater elements connected in 
parallel and to the 2j-volt 
winding of a filament heating 
transformer. It is also well to 
ground one side of this wind- 
ing. The F terminal of each 
tube socket should be con- 
nected to the receiver chassis 
while the F+ terminal of each 
tube socket should be ignored. 
The 2oo-ohm potentiometer 
should be eliminated and in 
its place a Carter 6ooo-ohm 
potentiometer used (the two 
center shields will have to 
have their corners clipped 
away to accommodate the 
new 6ooo-ohm potentiome- 
ter). Terminals 6 of the three 
left-hand r.f. transformers, 
which previously connected 
to the center arm of the poten- 
tiometer, should ground to the 
chassis. Theo.j-mfd. potenti- 
ometer bypass condenser is 
eliminated. The new potenti- 
ometer should be connected 
with one end to the chassis, 
the other end to the +90 
binding post, and the arm 
connecting to one end of the 
8-90 bypass condenser and to 
terminals 5 of the three right- 
hand r.f. transformers. Five 
Sovereign a.c. tubes are used, 
with a cx-371 (ux-i7i) type 
tube in the last audio stage. 
The two filament leads from 
this latter power tube socket 
are run directly to the 5-volt 
terminals of the filament 
transformer. The center tap of 



a Frost FT 64 resistance shunting the power tube 
filament connects through a 2ooo-ohm Carter 
fixed resistance to the chassis of the receiver or 
ground. A regular B supply, such as the Silver- 
Marshall 652A (which will also supply A poten- 
tial to the tubes) will then furnish B potential to 
the entire receiver, and A, B, and C potential to 
the second audio stage, while a 43-volt C battery 
will have to be used for the detector and the first 
audio stage (terminal 4 of the first audio trans- 
former should connect to the C Del. binding 
post of the receiver). 



3 S-M 63 1 Stage Shields . 
2 S-M ji6A Matched Condensers 
2 S-M 3166 Matched Condensers 
4 S-M 515 Coil Sockets .... 
3 S-M i i8A Matched Coils . . . 
I S-M i i6A Coil, Matched with Above 
6 S-M 511 Tube Sockets .... 
2 S-M 220 Audio Transformers . 
i S-M 221 Output Transformer . 
i S-M 632 Triple Link Motion . 
i Polymet o.2j-Meg. Grid Leak . 
i Polymet Resistor Mounting 
i Carter o.oo2-Mfd. Condenser . 
3 Carter 105 or Polymet Condensers, 

0.5 Mfd 

i Carter M-2oo Potentiometer (200 

Ohms) 

2 Carter No. 10 Tip Jacks 

i Carter H-J Resistor 

2 Marco Walnut Vernier Dials . 
i 636 Terminal Strip, ij x 1 1 inches . 
i Crowe 633 Drilled and Engraved 

Metal Panel, Size 7x21 Inches . 
i Crowe 634 Steel Chassis, Size 12 x 

igj x ij Inches 

i Carter No. 12 Antenna Switch 
i Carter "Imp" Battery Switch . 
i Coil Kellogg Fabricated Hook-up 

Wire, Screws, Nuts, Lugs, and 

Complete Building Instructions . 
Total 



$ 6.00 
9.00 
9.00 
4.00 
7.50 
2.50 
3.00 
16.00 
7.50 
2.50 

25 
.50 
.50 



2.70 

75 
.20 

25 
5.00 

2.OO 
8.50 

6.00 
.60 
50 



25 



$95.00 




THERE IS AN ADVANTAGE IN LEAVING ONE 

The antenna tuning stage, the only one of the four tuned stages not 
tion. By so doing, the coil pick-up is increased to a point where the 
with no antenna at all, and adequate volume obtained on the loud 



TUNED STAGE UNSHIELDED 
shielded, has purposely been left in this condi- 
receiver may be operated in apartment houses 
speaker when receiving powerful local stations 



ristocrat 




RADIO BROADCAST Photograph 

A SUITABLE LAYOUT THAT MAKES FOR SIMPLICITY OF CONSTRUCTION 

There are many possible variations of design for the new "Aristocrat," the layout here, in fact, not being exactly similar to that described in the text. The 
"deck," for example, is mounted away from the front panel in the model described, and one variable rheostat takes the place of the two ballasts shown in the 
photograph. New Eby sockets have been substituted for the older pattern ones shown, and binding posts are used for Antenna, Ground, and Loud Speaker 



By ARTHUR H. LYNCH 



EXACTLY two years ago RADIO BROAD- 
CAST first described the "Aristocrat" 
receiver. This receiver became unusually 
popular and many interesting letters were re- 
ceived telling of the good results that were ob- 
tained. It was a five-tube affair consisting of a 
stage of tuned radio frequency followed by a 
regenerative detector, and the audio circuit com- 
prised a three-stage resistance-coupled amplifier. 
Correspondence is still received from many 
readers regarding the receiver and evidently 
many "Aristocrats" are still giving good service. 
We do not intend in this article to describe a 
radically new "Aristocrat" receiver. The original 
circuit was carefully thought out and even 
though two years have elapsed since it was first 
described there are only minor ways in which it 
can be improved. An "Aristocrat" receiver care- 
fully constructed in accordance with the original 
description would be found selective, sensitive, 
and capable of giving good quality reproduction 
in the majority of cases; there are, however, a few 
rearrangements that might be made in the 
mechanical design which will make the construc- 
tion of this receiver simpler and better looking. 
Before going into the details concerning these 
suggested changes, a very brief description of 
the circuit in its revised form, with special ref- 
erence to the ways in which it differs from the 
original, will be given. The circuit diagram 
of the new " Aristocrat" is given in Fig. I. 
An important difference between the new 
and the old set is immediately evident to 
those who are familiar with the original 
circuit, i. e., that the antenna stage now 
uses a variocoupler instead of a tapped 
coil. Antenna tuning in the original re- 
ceiver was accomplished by means of 
the taps on the primary of the antenna 
coil and by proper use of this adjustment 
it was possible to obtain high efficiency 



from the receiver with various lengths of an- 
tennas. The new antenna coil of the "Aristo- 
crat" contains a secondary with primary inside 
it, variable coupling between the two coils ac- 
complishing the same results as did the taps in 
the original coil; with the new arrangement the 
.^adjustment can be made more readily and more 
accurately. The variable antenna coil is a dis- 
tinct improvement and should be incorporated 
in the new "Aristocrat" receiver and might also 
be used to advantage in receivers constructed 
according to the original circuit. 

The detector stage df the new "Aristocrat" 
remains the same as the original circuit. The 
audio amplifier is arranged so that somewhat 
greater voltage is placed on the plate circuits of 
the first two stages than was originally used. 
The new high-mu tubes should be operated with 
at least 135 volts on their plates. 

Simplicity of construction is the keynote of the 
new receiver. The improvements that have been 
made in the constructional features of the 
"Aristocrat" are, first, the use of a metal panel 
of special design and, secondly, a new and unique 
type of sub-panel construction. The special 
metal panel is designed to accommodate two 
variable condensers of the single-hole mounting 
type and the panel is also made for use with il- 
luminated dials. There are three additional holes 





PLATE 
VOLTAGE 


NEGATIVE C BATTERY VOLTAGE REQUIRED 


Power 


Semi-power 


Audio 


Radio 


45 
00 

135 
180 


16.5 

27 
40.5 


6.0 
9.0 

12.0 


'5 
3.0 


o 
3 





in the panel, the one at the left being for the 
antenna rotor control, the center one for the 
rheostat knob, and another hole at the right is 
for the regeneration control. This panel and dial 
combination can be used in constructing any 
number of circuit combinations where there are 
only two tuning controls and its use in the 
"Aristocrat" is a good example of its utility. 
The panel measures seven by eighteen inches and 
is a product of the Wireless Radio Company, 
of Brooklyn, New York. 

The new special sub-panel, or "deck" as it is 
called, has five Eby DeLuxe sockets mounted on 
it and audio amplifying equipment for a five-tube 
receiver. It is made of Westinghouse Micarta, 
and is built to accommodate ten binding posts. 
In the model illustrated the six-wire cable obvi- 
ates the use of six of these binding posts, connec- 
tion for the batteries being made directly to the 
wiring of the receiver by means of this six-wire 
cable. The audio amplifier is a three-stage re- 
sistance-coupled affair and both the resistances 
and condensers are held in place on the "deck" 
by clips so that constructors may use any values 
which they may prefer. The person who wishes 
to experiment can procure additional values of 
resistance and condensers than those which 
come with the deck and substitute them when 
desired. 

There are available many different an- 
tenna couplers and three-circuit tuners that 
may be used in the "Aristocrat." In the par- 
ticular receiver illustrated in the photo- 
graphs accompanying this article, Sickles 
"Aristocrat" coils have been used in con- 
junction with Cogswell condensers. The 
Cogswell antenna tuning condenser has 
been made in a very ingenious fashion. Its 
stator plates form one side of the neutraliz- 
ing condenser, while the other plate of the 
latter is mounted on a pair of hinges and is 



NOVEMBER, 1927 

adjusted by turning a small screw which pushes 
against an eccentric cam. It is all very small, 
very simple, convenient, and very effective, as 
well as being cheap. At the end of this article 
there is given a list of those parts used in the 
model that is illustrated, and the photographs 
and the circuit diagram should enable experi- 
enced constructors to build the receiver with little 
difficulty. 

NEW TUBES 

IT IS possible to procure an improvement in 
results from either an old or new "Aristocrat" 
by making proper use of the several new types of 
tubes that have become available since the 
"Aristocrat" first made its bow. A special de- 
tector tube, for example, may be used in the re- 
ceiver instead of a 201 -A type and it will increase 
the sensitivity and volume very considerably. 
In this case the detector grid return should go to 
negative A instead of to positive as indicated in 
Fig. i, unless a special Ceco type H detector 
tube is used, when no change is necessary. Ceco 
type G high-mu tubes should be used in the 
first and second stages of the audio amplifier. 
High-mu tubes of other manufacturers should 
not be used unless the condenser and resistor 
values are changed to comply with the specifica- 
tions of the individual makers. The output tube 
should be of the semi-power type with proper C 
and B voltages. Ceco makes special radio- 
frequency amplifier tubes which will give slightly 
increased gain in the r. f. stage. They are known 
as the type K tubes. These new tubes, without 
regard to any other improvements that might 
be made, will give greater distance, sharper tun- 
ing, and more volume than can be obtained when 
ordinary tubes are used. 

In the table accompanying this article there 
are given data on the C and B voltages that 
should be used on the various tubes. The column 
headed "Power" gives the voltages when a ux- 
171, cx-371, or Ceco ]-ji, is used in the output 
stage. The column head "Semi-Power" gives the 
required voltages when a ux-na, cx-ii2, or 
Ceco type F is used in the output. The voltages 
given under the column headed "Audio" refer 
to the high-mu tubes in the audio amplifier. The 
values given under the column headed "Radio" 
apply to either ZOI-A'S or special radio-frequency 



THE IMPROVED ARISTOCRAT 



47 




THE LYNCH "DECK 

Its utilization considerably simplifies receiver construction. 
The list of parts below tells just what the "deck" comprises 



amplifier tubes. If a 171, 371,0^-71 power tube 
is used in the output of the receiver, an output 
filter or output transformer should be used in the 
plate circuit of the tube to protect the windings 
of the loud speaker from the high plate current. 
As shown, the circuit is wired for a 1 12 or Ceco F 
type tube. C bias for the first two audio tubes is 
obtained by inserting a battery in the common 
grid lead at the point marked "X," the positive 
terminal of the grid battery connecting to nega- 
tive A. 

The results obtainable from the improved 
"Aristocrat" receiver do not suffer at all in 
comparison with the original set, while the total 
cost of building the receiver has been materially 
reduced. The automobile business is not the 
only one in which the honest claim that produc- 
tion methods enable you to purchase a better 
product for a lower price. In the case of the 
improved "Aristocrat," production methods 
have been applied to radio. 

Li, L; -Sickles "Aristocrat" Coils . 5 4-5 
Ci Cogswell Variable Condenser, 

Type A, 0.00035 Mfd. . . . 2.25 
Cj Cogswell Variable Condenser, 

Type B, 0.00035 Mfd., Neu- 



tralizing Condenser (Cs) At- 
tached 

C 3 , C Sangamo 0.004 Mfd. Fixed 

Condensers 

Four Eby Binding Posts . 
Six-Wire Cable . . . . 
Wireless Radio Company's 
Panel, 7 x 18 Inches, with 
Mounting Brackets, Illum- 
inated Dials, and Filament 

Rheostat (Ri) 

Two Kurz-Kasch Knobs . 
Lynch Deck, Including the 
Following Parts, Mounted and 
Ready for Wiring: 
Westinghouse Micarta Panel 
Seven Resistor-Condenser 

Mounts 

R 2 , R 3 , RI o.i-Meg. Metallized 
Resistors 

R 5 , R 6 , RT o.5-Meg. Metal- 
lized Resistors 
R 2-Meg. Metallized Resistor 
C 7 , C s , Ci o.oo6-Mfd. Tubular 
Condensers 

Ce o.ooo25-Mfd. Tubular 
Condenser 
Five Eby DeLuxe Sockets 

Total 



2-75 

1.20 
.60 
.60 



4.50 
.50 



12.50 



f , Inside Terminals of Secondaries , 
A C 5 




THE CIRCUIT DIAGRAM OF THE "ARISTOCRAT" RECEIVER 




uppressin 



Interference from Motion Picture Theatres, Telephone Exchanges, Arc 
Lamps, Incandescent Street Lamps, Flour Mills, Factory Belts, Electric Warm- 
ing Pads, Precipitators, Etc., Is Discussed, and Remedies Are Suggested 

By A, T. LAWTON 



A THOUGH this article is really the second 
of a series, the first of which appeared 
in the September RADIO BROADCAST, it 
is nevertheless complete in itself, and the 
reader who is suffering from interference of 
any of the forms outlined here will profit con- 
siderably from a study of this paper. The data 
presented here result from a two-and-a-half-year 
study conducted by the author in more than 132 
cities. The forms of interference covered in the 
September article were those due to oil-burning 
furnaces, perhaps the most common source of 
man-made static, X-ray equipment, and dental 
motors. The first kind of interference to be con- 
sidered here is that originating at motion picture 
theatres. 

MOTION PICTURE THEATRES 

THE radius of interference from this source is 
ordinarily about 200 yards, occasionally 
greater, depending on exterior wiring. In the 
great majority of cases the direct-current genera- 
tor is responsible for the trouble. Contrary to 
popular belief, the arc lamps themselves cause 
practically no interference; in fact, there is often 
less disturbance with the arcs lighted than before 
they are "struck," j. e., 

with the generator run- Motor 

ning unloaded. The dif- 
ference in certain cases 
is decided, absorption of 
the interference occur- 
ring as soon as the arcs 
are put on. 

Fig. i shows a method 
used to eliminate this 
interference with success 
in actual practice. Five- 
ampere fuses are used. 
If the commutator is 
badly worn, it should 
be turned down in a 
lathe, and we might re- 
mark here that the quality of the carbon brushes 
used have a noticeable effect on the intensity of 
commutation interference. 

Squirrel cage induction motors are in common 
use for driving these generators and, ordinarily, 
give no trouble unless some defect is present. 



TELEPHONE EXCHANGES 

[T IS probable that in most cities interference 
' from this source has been cleared up. The 
larger operating companies have been active in 
this regard, but in smaller towns and rural com- 
munities much trouble exists. On the larger type 
motor ringers, high-tone and low-tone (sometimes 
referred to as trouble tone and howler) circuits 
are mainly responsible. Complete elimination is 
secured by inserting a choke coil in each of the 
two brush leads, close up to the machine. De- 
tails of the coil required are shown in Fig. 2. 

Complications arise if connection is made at a 
distance of more than four inches from the 
brushes incomplete elimination resulting. 

The greatest offenders in the category of tele- 
phone ringing apparatus are pole changers and 
frequency converters. These constitute standard 
equipment in thousands of small exchanges; 
in some larger exchanges they are operated only 
after 10 p. M. when the rush hours have passed. 
The interference is of a rapid clicking nature and 
may carry half a mile or more, depending on 
the proximity and layout of the city distribution 
and telephone wiring. 

For pole changers, definite and conclusive re- 

, 2-mfd. Condensers 




A.C. Supply 





A-*" B-%" C-V D-254" E-%" 
Hardwood Bobbin, approx. 300 
turns No.22 (about 125 ft.) 

FIG. 2 

Constructional details for the choke coils recom- 
mended for elimination of interference originating 
in telephone exchanges 



FIG. I 

suits are obtained by inserting the coils described 
in Fig. 2 in the ringing leads and at least 95 per 
cent, of the trouble disappears. Up to the present 
we know of only one instance where this method 
failed and peculiarly enough, a simpler method 
cleared up the trouble. A single one-half micro- 
farad condenser bridged across the contacts gave 
loo per cent, elimination. 

Frequency converters are a different proposi- 
tion, operating off a. c. instead of d. c. as in the 
case of pole changers. The surge trap applicable 
to pole changers gives only 50 or 60 per cent, 
reduction. 

A special surge trap is made up for this source 
by companies manufacturing the frequency con- 
verter, and it will be found more economical in 
the long run to purchase this complete rather 
than endeavor to make it up locally. For all 
practical purposes, complete elimination is ob- 
tained through the installation of the special 
surge trap. 

Automatic telephones, now coming into such 
general use, contribute their little quota of dis- 



turbance. Usually they affect radio receivers 
only in the same residence where the dialing 
operation is being carried out, although several 
cases are on record where radio sets of next-door 
neighbors were also affected. 

A single condenser of one microfarad capacity 
placed across the dialing circuit will cut out the 
clicking noise and does not appear to have any 
detrimental effect on the speech transmission 
or proper functioning of the line. However, per- 
mission of the telephone company should be ob- 
tained before making any attachments. 

ARC LAMPS 

C TRANCE as it may seem, flickering arc 
-5 lamps cause practically no radio interference. 
If the arc is jumping violently, however, then 
clicks are recorded on radio receivers in the 
vicinity; a short distance away interference is 
not material. This doesn't mean that arc lamps 
cause no disturbance. On the contrary, during a 
recent investigation one arc lamp practically 
killed radio reception for eleven city blocks along 
one street. It was burning perfectly steadily and 
showed no sign whatever of defect. 

The characteristics were slow clicking in dry 
weather, fast clicking in moist atmosphere, and 
rapid clicking during rainy weather. On a five- 
tube set with loud speaker, the noise was violent, 
resembling very much the operating of a pneu- 
matic hammer. The source of trouble here was a 
minutefissure in the composition head ring which, 
filling up with moisture, caused a high-resistance 
short across the 4Ooo-volt lines. Evidently the 
spark dried up the moisture at each crossover, 
and time was required for the path to reform, 
otherwise we should have gotten steady buzzing 
here. 

During all the days this case was under obser- 
vation not once did it come on coincident with 
the lighting of the arcs, but always twenty 
minutes or twenty-five minutes afterward. It 
took time to develop, possibly a slight heating 
and consequent expansion of the parts being 
involved. 

If arc lamp interference comes on directly the 
lamps are lighted the source is very likely to be 
line trouble, such as wires scraping on iron 
bracket arms, loose splices, etc. 

In many localities where it is prevalent arc 
lamp circuit interference starts up before the 
lamps are lighted, perhaps twenty-five or thirty 
minutes previous to lighting, and it is quite 
regular every evening. 

This is caused by the rectifying tubes in the 
power house or sub-station. These tubes are 
"warmed up" for service prior to the line being 
switched in; the operation takes twenty-five 
minutes or so, and radio-frequency surges pass 
out on the line despite the open switch, so even 
before the lamps are actually lighted interference 
starts. Intensity of the interference is increased 
when the lights come on and continues all night, 
until the daylight shut-down. Generally speak- 
ing, new rectifying tubes do not give trouble, nor 
older ones, paralleled. Overloaded tubes, how- 



SUPPRESSING RADIO INTERFERENCE 



49 



ever, or those which have become hard through 
long usage, are liable to set up interfering 
surges that will travel long distances over the 
system. 

The obvious thing to do with a defective lamp 
is to have it repaired; the same thing applies to 
line defects. Rectifying tube disturbance, by 
far the worst trouble because of its continuous 
nature and wide range, can be cleared up by 
putting a choke coil as described in Fig. 3, in 
each outgoing d. c. feeder. 

Two hundred turns of No. 16 d. c. c. wire are 
required on a wooden cylinder 35 inches diameter 
and about 12 inches long. Longitudinal slots are 
cut in the cylinder for insertion of fibre strips 
which keep the wire off the wood and provide 
adequate heat radiation facilities. This is for 
4-ampere arcs; for 6-ampere arcs it may be as 
well to use No. 14 wire. 

It seems that in certain instances of this na- 
ture, seventy-turn chokes were large enough to 
give satisfactory elimination; in the particular 
case in mind they were ineffective. 

INCANDESCENT STREET LAMPS 

IT MAY come as a little surprise when we say 
that, given any city where the street lighting 
system consists of, say two thousand series arcs 
and two thousand series incandescent lamps, on 
various circuits, more radio interference will be 
caused by the incandescent lamp circuits than 
by the arc system. 

This is due to less careful installation in the 

case of the incandescent system not because 

of any inherent defect. The condition is general. 

Of one hundred cases of radio interference due 

to faults on series incandescent lighting systems: 

42 were caused by down-lead wires scrap- 
ing on the iron brackets. 
1 5 by loose connections of the wires at the 

lamps. 
10 by internal defects in the lamp fixture 

proper. 
10 by partial shorting of the wires in conduit 

prior to connection at the lamp. 
9 by poor line splices. 
5 by leakage or spitting at the disc fuses in 

the lamp head. 

5 by lamps loose in their sockets. 
4 by defective mercury or other type auto- 
matic time switches. 

It may be remarked here that sources on a 
series lighting system giving rise to radio inter- 
ference are most difficult to locate. What occurs 
at a defective lamp seems to be duplicated in 
many lamps either side of the faulty one; in- 
tensity values of the interference are misleading 
and very careful observation is required. 

FLOUR MILLS 

JN PRACTICALLY every Hour mill the chlorine 
* process of bleaching has been superseded by 
the electrical method. This consists of a twenty- 
thousand volt spark oscillating directly in the 
path of a blast of air, the latter becoming ozonat- 
ed, passes on to the grain in process of crushing. 

Direct radiation is confined to a few hundred 
feet. The source, however, is a vigorous one and 
distribution wiring carries the disturbance to 
great distances; it is capable of mutilating radio 
reception practically all over the average small 
town. 

Methods of elimination are simple and definite. 
One hundred-and-fifty turn choke coils wound 
on three or three and a half inch tubing will 
kill at least 85 per cent, of the noise and will not 
interfere in the least with normal operation. 

Operating current here is 12 to 15 amperes; 
if the coils are not banked, No. 10 wire will be 
suitable. To conform to Electrical Inspections 



requirements, enclosure of the coils in a standard 
outlet box is recommended, the knockout holes 
of which have been opened and covered with 
fine wire gauze. This latter affords good ventila- 
tion while preventing grain dust accumulating 
on the coils. 

Self-contained bleachers of the arc type cause 
no trouble. They are, however, being rapidly 
displaced by the more efficient spark type. 

FACTORY BELTS 

HIGH-SPEED belts are a fruitful source of 
radio interference, especially noticeable in 
cold, dry weather. Friction between the pulleys 
and belting causes a static charge to form on the 
belt and this, after rising to a high potential, 
will spark to nearby metal objects, setting up a 
"crackling" noise in the receiver. 

As most heavy rotary machines are well con- 
nected to ground one would imagine that this 
static charge would filter away gradually, and 
fail to build up to any material potential. The 
fact is, and it can be demonstrated, that the film 
of oil in the machine bearings is sufficient to 
insulate the rotating parts from ground. 

A "static collector" is used to get rid of this 
trouble. It consists of a wiping contact of springy 




FIG. 3 

metal, at all times resting on the belt in motion 
and permanently connected to earth. 

A metal laced belt can set up quite a loud click- 
ing interference. Every time the metal lacing 
passes over an iron pulley the click is heard. 
No such effect is noted, of course, where wooden 
pulleys are used, but in the cases cleared up we 
simply removed the metal lacing and substituted 
rawhide. 

ELECTRIC WARMING PADS 

WHETHER interference from this source 
is to be regarded as serious or not depends 
on how far away you live from the offending pad. 
The radius is about two dwellings either side 
of the one in which the pad is being used, assum- 
ing that the houses are close together. 

Little thermostats inside the pad automati- 
cally break the supply current when the pad 
becomes sufficiently heated and switch it on 
again when the elements cool sufficiently. This 
alternate opening and closing of the no-volt 
supply line sets up clicks which are extremely 
annoying to broadcast listeners in the immediate 
vicinity. 



Intensity of the trouble varies with the make 
of pad and also with length of service. It seems 
that corroded or burned contacts are responsible 
for most of the trouble and before going to the 
expense of purchasing condensers, etc., it is usual 
to open the warming pad and readjust the ther- 
mostat contacts after cleaning them up properly. 

A different problem is presented in the case of 
hospitals. Take a literal, specific example: Two 
hundred patients, two hundred pairs of tele- 
phones (no loud speaker allowed) and, incident- 
ally, two hundred warming pads (one for each 
cot), Were in use. Every time a patient gets rest- 
less and kicks out his feet he jars the pad thermo- 
stats and treats the other hundred and ninety- 
nine to a series of sharp clicks usually resulting 
in reciprocation. 

Substitution of quiet types for the noisy ones 
and condenser absorption would seem to be the 
best recommendation. 

PRECIPITATORS 

THIS apparatus is used in the treatment of 
various ores as well as for the purpose of 
smoke and dust precipitation. Its radio interfer- 
ence can be heard ten miles; at five miles it hurts 
reception and in the vicinity of the plant, normal 
reception is impossible. 
As in the case of the 
notorious oil-burning 
furnace, methods of 
elimination which clear 
up the trouble in one 
installation fail to give 
the desired results when 
applied to another 
plant. 

Several cases have 
been cleared up ucing 
high-frequency chokes, 
i.e., placed in th^ high- 
tension circuit. The coils consist of 500 turns of 
No. i$ or No. 20 bare or covered wire on a tube 
three and one half inches in diameter. Individual 
turns should be spaced about one eighth inch 
apart except at the ends, where one-quarter inch 
spacing is recommended. 

Fig. 4 shows an arrangement which has given 
satisfactory results. It may be necessary in other 
cases to split this 500 turn choke, i.e., putting 
250 turns near the rectifier and 250 near the 
treater. 

In the types where the high-tension energy 
for the rectifier is obtained through transformer 
action direct from a transmission line, inter- 
ference is naturally heavie than that experienced 
from the more or less self-contained motor gen- 
erator type although the actual energy in the 
former is less than in the case of the latter. 
Average energy values will be about 70 milli- 
amps. at 30,000 volts and 80 milliamps. at 50,000 
volts, respectively. 

Considerable experimental work has been 
carried out by different precipitation plants in 
this connection and while special treatment was 
found necessary in several instances practically 
all cases investigated have been cleared up. 



Rectifier 




Supply 



- Chokes ..- 



- -Treater 



G W 



FIG. 4 



AS IHh 




MDCASIKR . 







KY C:AKI OKFHFR 

Drawing by Frantyyn F. Stratford 

Putting Freak Broadcasting in Its Place 



IN ALL human affairs the tendency is toward 
quiescence and boredom. Among vigorous 
peoples this drift toward monotony is resisted 
by a constant seeking for innovations. Now and 
then some fruitful bit of originality rewards the 
quest. In the main, however, the innovations 
are failures. They have no deep roots in human 
desires or interests, and, after the first glance, 
they amuse the normal spectator even less than 
the old shows he is weary of. The spirit is praise- 
worthy, but the results are dreadful, especially 
in the arts. Consider the poets, for example. 
Here and there one of them, distressed by his 
inability to convince the world that he is another 
Shelley, decides to be entirely original by print- 
ing a magazine of verse with a fake Nujol ad- 
vertisement on the cover, no capital letters, and 
half the words upsidedown. His originality is 
hard on the compositors. To be original, in the 
sense of doing something that is not commonly 
done, is very easy. To that degree you can be 
an exponent of novelty, by entering the nearest 
drug store and ordering a pineapple soda with 
chocolate cream. But to be fruitfully original 
requires more than twenty cents. 

We are similarly beset in the art of broadcast 
entertainment. The innovations are many, but 
most of them are of the twenty-cent variety. 
1 do not intend to itemize all the varieties of freak 
broadcasting; it would be impossible, and, be- 
sides, a certain portion of this department is 
consecrated to sensible subjects. A few samples 
will suffice. 

The broadcasting of alleged disembodied 
spirits seems to me to fall into the category of 
futilities politely hinted at above. I have no 
animus against the spirits as such. It is true that 
I have never seen one, and, since studying psy- 
chopathology, have doubted their existence. 
Nevertheless, as 1 have not seen everything in 
the universe, and don't expect to, I acknowledge 
that such things as ghosts may exist. But why 
broadcast them? If a 
ghost wants to see me, 
let him or her call on 
me at my office, or in 
the dark reaches of the 
night. But as a broad- 
cast listener, I like to 
be entertained. As a 
broadcast listener, I 
also object to the im- 
putation that 1 am a 
total ass. No doubt 1 
am an ass in some re- 
spects, but not to the 
extent that I can be 
kidded, on hearing the 
tinkling of glass, a noise 
like a $6 saxophone, 
and some mumbling 
through my loud 
speaker, into believing 
that authentic goblins 
are disporting them- 
selves in the studio of 
the puissant broad- 
caster who is striving to 
instruct me. And, when 



a committee of spiritualist investigators assure 
me that everything is aboveboard, I guffaw 
openly at their discourse. Who are they to tell 
me so? What do they know about the tricks of 
broadcast transmission? 

The method used in broadcasting the shades 
is to turn on the microphone and, with the studio 
doors locked and no one in the room, to listen 
for mysterious sounds on the station carrier, 
which is assumed to be quiet. The investigating 
committee watches the studio doors and snoops 
around otherwise at their discretion. But can 
they assert with any semblance of plausibility 
that they know all the sources of input to the 
speech amplifiers of the transmitter? Nothing 
could be simpler than to rig up an additional 
microphone somewhere in the building and, 
paralleling it with the transmitter in the empty 
studio, to broadcast any sounds one cares to. 
Not even that is necessary. One of the operators 
can tap a tube in the speech amplifier and make 
noises which will seem inexplicable to the ghost- 
chasers. The business of spiritualistic investiga- 
tion is at best full of complications, and to 
complicate it further by adding the technical in- 
tricacies of a broadcast transmitter is beyond all 
sense. Whether there is fraud or not and cer- 
tainly in connection with struggling stations 
avidly bent on cadging every possible square 
inch of newspaper space the possibility of decep- 
tion is not remote the pretence of scientific 
investigation under such conditions is simply 
silly. The broadcast listeners may not be New- 
tons, Goethes, and Mommsens, but they are not 
voodoo worshippers either. The studio manager 
who first conceived the idea of broadcasting 
spirits may have been original, but he omitted 
to mix a few brains with his originality. 

Even more infantile is the menagerie broad- 
casting stunt. The only justification I can see 
for it is in connection with a children's hour. 
The noises made by sea lions and rhinoceroses 



are neither agreeable nor intellectual, and, being 
full of steep wave fronts and tones outside the 
band of transmittable frequencies, they don't 
get over anyway. If a man roared into the trans- 
mitter it would sound as much like a lion when 
it got through the loud speakers as if a lion did 
the roaring. 

As one listener, 1 ask to be spared such buf- 
fooneries. I respect the urge for originality, but 
it must take a more convincing shape than in 
such procedures, which have no other use than 
to get some station's publicity matter a transient 
hearing. If there is nothing interesting left to say, 
and nothing beautiful left to play, my counsel is 
to shut down the transmitter and economize 
on electricity at the rate of three cents per kilo- 
watt hour. 



Background Noises 



M 



R. A. S. DANA of Seymour, Connecti- 
cut, writes us as follows: 




'LET THE GHOST CALL AT MY OFFICE 



The better grade of broadcasters have made 
such improvement in their quality that there is 
but one factor which could be improved in so 
far as my ability to judge quality goes. 

Is it not possible for them to reduce or elimin- 
ate the noise background which accompanies 
the transmission? In other words, cannot the 
equipment be improved so that it is not possible 
to tell when a station is on the air unless speech 
or music enters the microphone? According to 
present standards, it is easy to locate and tune-in 
a station when they are not broadcasting simply 
by the racket which occurs when the station is in 
tune. 

Mr. Dana seems to think that the noise in 
question is all generated at the transmitter. 
Actually there are three possible sources. In 
some cases all are in evidence, and in others none. 
Background noise may have its inception 
right at the microphone. The transmitter itself 
has a degree of inter- 
nal hiss caused by cur- 
rent passing through 
the carbon in the 
case of a microphone, 
and by tube irregu- 
larities in the first 
stages of the ampli- 
fier associated with a 
condenser transmitter. 
But if the microphone 
is well designed and 
the carbon of high 
quality, and not too 
old, the sensitivity 
to external sounds 
is so great that the 
hiss is seldom audible. 
In the case of speech 
input some slight hiss 
is usually observable, 
and occasionally 
during pianissimo 
passages of musical 
performances, but 
with proper micro- 
ohone care the internal 



NOVEMBER, 1927 




Q 

3 






FIG. I 

noise level is negligible. If the tubes in the asso- 
ciated amplifier of a condenser transmitter are 
carefully picked this instrument is practically 
noiseless with normal inputs. Of course any type 
of transmitter will pick up room noises, and 
broadcasters cannot always secure their material 
in perfectly quiet places. But in general we may 
say that most well regulated stations transmit 
practically noise-free modulation. By that I 
mean that at a distance of a few feet from the 
monitoring cone in the station, which is assumed 
to emit a loud signal during modulation, no 
sound is audible in the intervals. Of course, by 
placing one's ear on the cone one can hear plenty 
of rustle, but that is going out of one's way. 
It is like saying that the alarm clock in my house, 
which I can hear ticking 33 feet away if I listen 
hard enough, is causing a disturbance which 
should be eliminated. 

But after leaving the transmitting antenna, 
the modulated wave must run the gauntlet of 
electromagnetic disturbances in the medium 
between transmitter and receiver. The metaphor 
1 have used here may be an unfortunate one, if 
it confirms the popular supposition that the car- 
rier, in some mysterious way, picks up noises on 
its journey through space. People jump to this 
conclusion because they find, in tuning their 
receivers, with the sensitivity control well down, 
that they hear nothing over a certain section of 
the broadcast frequency range, and then, run- 
ning across a blank carrier, they get a more or 
less audible background. The actual sequence 
here is more along the following lines, however: 
The receiver has been picking up slight disturb- 
ances static, distant violet-ray machines, trans- 
mission lines, bells, and the like, right along, but 
at a level below audibility, when the receiver 
sensitivity is low. But the carrier coming in in- 
creases the receiver sensitivity through its hetero- 
dyne amplification, hence the noises come up 
when the receiver is tuned to a carrier. Of course 
neighborhoods vary in the relative strength of 
external disturbances, and anywhere there is a 
variation with time; normally the atmosphere 
may be quiet, but when there is local lightning 
plenty of crashes and rumbles will be picked up 
by all receivers. However, Mr. Dana's question 
probably does not include these relatively rare 
periods of acute disturbance. 

Finally we must take into account the internal 
noises of the receiver itself. There is a tendency 
for slight gaseous irregularities in the radio 
frequency tubes to be amplified through each 
successive stage until quite a noticeable rustle 
results in the loud speaker. But if the tubes are 
properly exhausted there should be no trouble 
from this source. I have an eight-tube receiver, 
and, in testing it as 1 write with the sensitivity 
control all the way up and the loop removed to 
eliminate r.f. input, I am unable to hear any 



CARRIER FREQUENCIES ON TELEPHONE LINES 

sound whatsoever. With the loop in position I ^ 

can hear the elevator motors in nearby apart- 
ments and a medley of undifferentiated noises, 
but then in practice 1 should never think of using " ^ 
the receiver in this state of excessive sensitivity. 
The receiver may also develop internal noises 
through regeneration at radio or audio frequency, 
or through an impure plate or filament supply. 
When at a low level, many such sources of dis- 
turbance manifest themselves as rustling or 
murmuring sounds which may be ascribed to the 
broadcast transmitter. 

The increase of transmitting power has un- 
doubtedly reduced background noise in radio 
reception, by permitting the use of less stages of 
amplification and lower sensitivity at the re- 
ceiver, for the same signal volume. But the factor 
of modulation depth comes into the problem 
forcefully. A weakly modulated carrier simply 
amplifies static and interference at the expense 
of its intelligence-bearing side bands. Deep 
modulation is highly desirable on this account, 
and limitations on adequate modulation which 
means 80-90 per cent, peaks, are as bad as inade- 
quate field strength. Of course the best thing is 
to get rid of the carrier altogether, but that is a 
technical step feasible, at this stage, only in 
radio circuits professionally operated at both 
ends. 




51 



Circuit Efficiency 



FREQUENCY 




FREQUENCY 



Output Currents 



Abstract of Technical Article. VII 

Making the Most of the Line A Statement 
Referring to the Utilisation of Frequency Bands 
in Communication Engineering, by Dr. Frank 
B. Jewett. Presented before Philadelphia 
Section of the A. I. E. E. on October 17, 
1923. Reprinted May, 1924 by Bell Telephone 
Laboratories, Inc. 

(Continued from October RADIO BROADCAST) 

IN A carrier-current telegraph system free of 
capacity and inductance, a series of dashes 
made at the transmitting key will be repro- 
duced accurately as oscillations of the carrier 
frequency within a rectangular envelope, as 

.--Band Filter 
_i__-- Resonant Circuit 

U f 

S 
^ 
o 

FREQUENCY 
FIG. 3 

shown in Fig. i-A. If, now, inductance and cap- 
acity be inserted into the circuit so that it be- 
comes resonant to the carrier frequency, the 
same keying action will produce, at the receiving 
end, a trace like that of Fig. i-B. The circuit 
now has a certain "stiffness," so that it takes 
some time for it to reach the full amplitude of 
oscillation at the carrier frequency, and again, 




<M/-pJUb-nJ!a/-r\flll/- S I 



LOW PASS FILTER 
HI I II I II I lh- 



HIGH PASS FILTER 



FREQUENCY 




FREQUENCY 

A 



BAND PASS FILTER 



FREQUENCY 



FIG. 4 



FREQUENCY 
FIG. 2 

after the key has been opened, the oscillations 
continue in a decaying wave train like that of 
the old spark transmitters. The faster the rate of 
signalling, the more serious the distortion; if, 
for example, dots and dashes are made too 
rapidly, the amplitude will never drop to zero at 
all, as shown in Fig. i-C, although complete 
breaks are made at the key. The reason for this 
appears in Fig. 2. The top curve (A,) is a typical 
resonance peak, showing how the circuit effi- 
ciency, by virtue of the tuning effect, varies with 
frequency. This property, as we saw in the first 
instalment of this abstract, is a valuable means 
of frequency discrimination. But the effect also 
involves changing the amplitude of the various 
components shown in the input currents of Fig. 
2-B to the output currents of Fig. 2-C. As we 
saw in the earlier ciscussion, 2-B includes the 
components of a square-topped wave. The 
suppression of the higher harmonics and the 
exaggeration of the carrier frequency have de- 
stroyed the rectangular wave shape. We could 
get it back by sacrificing selectivity by broaden- 
ing the circuit but then we sacrifice also the 
power of discrimination on which we must de- 
pend if we are to make the most of the line. 
Obviously what is needed is a form of frequency 
discrimination which will pass a certain band of 
frequencies with substantially equal efficiency, 
and cut off sharply frequencies outside of this 
band. Reactive networks known as "filters" 
have been devised by telephone engineers to 
give this effect. Fig. 3 shows the difference in 
transmission characteristics between a resonant 
circuit and a filter designed to pass a band of 
frequencies in the same neighborhood. Fig. 4 
illustrates the principal types of filters and their 
respective properties. Such circuits are of the 
utmost importance, not only in the practical 
communication arts, but also in investigations 
of the nature of speech and music. (Cf. Jones: 
"The Nature of Language," abstracted in April, 
1927, RADIO BROADCAST.) 

Besides the property of selective frequency 
transmission, the characteristic impedance of 
such networks is of importance. Fig. 5 illustrates 
two types of band filter with substantially simi- 
lar elements, but designed for different connec- 
tions. A is feasible for parallel connections, the 
impedance being very high for all frequencies 
save the band the network is designed to pass. 
But when the terminating elements are as 
shown in B the impedance to frequencies other 
than those in the transmitted region is low, so 
that such filters may only be connected in series. 
By the use of networks suitably designed and 
connected a number of carrier frequencies may 
be delivered to a line without mutual absorption, 



52 



RADIO BROADCAST 



NOVEMBER, 1927 



and then separated for individual demodulation 
at the receiving end of the line. 

By the methods described above the multiplex- 
ing of lines is accomplished. As an example, 
Jewett gives the schematic circuits for the multi- 
plication of telephone channels over an open wire 
toll line. 

Up to about 100 cycles per second the line is 
available for d.c. telegraph purposes. Above this 
point comes the d.c. telephone band with its 
300-2800 cycle range, approximately. From 
3000 cycles up to about 35,000 may be used for 
carrier-current telephone channels. It is custom- 
ary in most cases to use the frequencies below 
20,000 cycles for transmission from east to west, 
and those above this figure for transmission from 
west to east. The attenuation suffered by cur- 
rents in the upper range is naturally greater and 
correspondingly higher amplification is required 
for equal received energy. A band about 2500 
cycles wide must be allowed for each carrier 
channel, and a space of 1000 cycles is required 
for separation between channels with band filters 



Normal Line -._ 




Trunk Line 



Receiving Channels 
WEST TERMINAL 

FIG. 6 

possessing the usual discrimination characteris- 
tics. 

Fig. 6 shows one terminal of a carrier tele- 
phone system. At this end we shall follow out the 
steps involved in multiplex transmission. As the 
line is also used ford.c. telegraphy and telephony, 
a low-pass filter is inserted in the metallic circuit 
to prevent the carrier frequencies from reaching 
subscribers through the toll board. Likewise in 
the carrier line, a two-way high pass filter pre- 
vents the currents below 3000 cycles from being 
absorbed in the carrier apparatus. Three pairs 
are shown leading from the toll board to the 
carrier equipment. In the case of the channel 
which is shown in heavy lines, the voice currents 
pass first through a low frequency circuit which 
permits the passage of current between the nor- 
mal line and either the transmitting or re- 
ceiving side of the carrier equipment, but which 
blocks currents between these two halves in a 




FOR PARALLEL CONNECTION 





J_ 



JU 

10'- 
10' - 




pWir Communication 
JMM 
nnptaie Musical Scale. 


64 Fc 

256FcMMid 


Vf- 


... 


PL: 

T'WlWtOTt 1. - i 


1024 FC I Pi 
40% FC" 
16384 Fc* 1 


IflP- 

10'- 




Commercial 
&'oKkKt m g > Radio Communication 


"^JLES OCTAVES 


10'- 




Amateuf 
SfMtill S*rv 




\t. 








If. 




Shorter Hertzian Waves 




10 : '- 








Itf 1 - 








10- 








10 :i - 




Infra Red 




io ; <- 




I '.}** ?(?." J! 1 ;?"* Ei>. n5BhM 




10 ! ''- 

iir- 


. 


-.- = .-.- - J -,_... . _ vB*JS7 V'SiDie SpeCUTJm 
Uftra-Violet 




iv-- 




Very Soft X Rays 




VS-- 


_ 


X-Rays 




10"- 


.... 


Gamrr^Rays 




irr- 


.... 







FIG. 8 



FOR SERIES CONNECTION 
FIG. 5 

vertical line. The importance of this feature will 
appear later on. When the subscriber on this end 
talks the voice currents generated in his desk 
set modulate the output of one of the carrier 
oscillators, and, passing through a band filter, 
which selects one of the side bands, merge with 
other side bands and go to the trunk line. First, 
however, it will be noted that they pass through 
a low-pass filter, designed to transmit the east- 
bound group of frequencies below 20,000 cycles. 
This filter prevents the transmitting carrier 
circuits from absorbing incoming energy in- 
tended for the receiving channels. 

At the other terminal of the line, sketched in 
Fig. 7, the receiving process may be traced. 
Again the common line is connected to a low- 
pass and a high-pass filter. At this crossroads 
the low-pass filter selects currents associated 
with d. c. telegraphy and telephony and admits 
them to the composite set. The high pass filter 
selects the carrier side bands coming in from the 
west terminal and conducts them to the group- 
ing filters, where the incoming currents are led 
to the receiving modulators. Again a band filter 
selects the appropriate side band for each branch. 
The demodulated currents pass to their respec- 
tive jacks on the toll operators' board, through 
the low frequency balancing circuits. If it were 
not for these circuits obviously the received 
voice currents would be sent back through the 
transmitting carrier equipment, instead of being 
confined to the subscriber at the east terminal. 

Jewett sums up the process physically as 
follows: 

We have . . . followed through, from one toll 
board to the other, a particular signal and have 
seen how it is moved about on the frequency scale 
to a position which identifies it from other similar 
signals, how it is associated with such signals on a 
common line, transmitted to the distant terminal, 
isolated at the receiving end from these other 
signals and finally restored to its original position 
upon the frequency scale. 

When a circuit is to be multiplexed for tele- 
graph the range between 
3000 and 10,000 cycles is 
normally devoted to this 
purpose. The directional 
dividinglineisthen usually 
at 6000 cycles, frequen- 
cies below this point being 
used for transmission from 
west to east and frequen- 
cies above 6000 for trans- 
mission from east to west. 
Various combinations of 
carrier telephone and tele- 
graph are possible. One 
layout shown in Jewett's 
paper comprises the fol- 
lowing facilities: 2 full 
duplex normal telegraph 
channels; i normal tele- 
phone channel; 10 full 
duplex carrier telegraph 



channels; 3 carrier telephone channels. This 
amounts to a total capacity of 24 one-way 
telegraph messages and 7 one-way telephone 
messages for one pair of wires. 

Carrier channels, employing currents of rela- 
tively high frequency, are subject to correspon- 
ingly greater attenuation and must sometimes 
be provided with repeaters at points where low 
frequency channels do not require amplification. 
At such a repeater station the low frequency 
currents are carried around the carrier repeaters 
by means of two low pass filters and a wire cir- 
cuit. By means of group filters the telegraph 
channels are separated from the telephone chan- 
nels, and finally each individual frequency is 
led by a band filter to the repeater designed for it. 

Jewett ends his paper by a brief discussion of 
the multiplexing of radio circuits. He points out 
that at the high frequencies employed in radio 
transmission the range covered by a simple 
resonant circuit is usually sufficient to include a 
band wide enough for good telephonic quality, 
so that filters, with their rectangular characteris- 
tics, are not required. 



Trunk Line 




Receiving Channels 

EAST TERMINAL 
FIG. 7 

A spectrum chart of electromagnetic waves, 
with frequency plotted on a logarithmic scale, 
taking in everything from the commercial d. c. 
telegraph to the gamma rays of radium, is also 
supplied, and is reproduced here as a matter of 
general interest (Fig. 8). 

Auditorium Acoustics 

THE Celotex Company of 645 North Michi- 
gan Avenue, Chicago, have issued a good- 
sized booklet describing their patented 
sound absorbing material, Acousti-Celotex, 
which, among other applications, has found use 
in various broadcasting studios in this country. 
About eight pages of the pamphlet are devoted 
to a fairly technical discussion of "Analyzing the 
Acoustics of Auditoriums," the subject matter 
covered being the same as that of our article on 
"Studio Design" in the June, 1927, issue of 
RADIO BROADCAST. The former article, being 
considerably longer, goes into more detail and 
takes up special problems, such as the effect of 
stage openings and balconies in auditoriums, 
factors influencing distribution of sound, etc. 
Naturally Acousti-Celotex is the absorbing ma- 
terial used in the examples, but the discussion is 
commendably general and only a small portion 
of the space in this section is devoted to adver- 
tising the manufacturer's product. The pamphlet 
should prove of interest to many broadcasters 
and acoustic engineers. 

A word about commercial aspects in such mat- 
ters. This department does not recommend 
specific products to its readers, but neither does 
it labor under any phobia as regards commercial 
publications. It is glad to receive them, and, 
when the material appears interesting and useful 
to technical broadcasters, in the personal judg- 
ment of the one who happens to be writing these 
papers, they will be mentioned at suitable times 



RADIO BROADCAST ADVERTISER 



53 



ALUMINUM 

AT THE RADIO SHOWS 




T 



year's Radio Shows 
demonstrate that Aluminum 
has been adopted for shielding 
by more of the leading manu- 
facturers and Radio Engineers 
than ever before. 

The RGS "Octa-Monic" is an 
outstanding example of the use 
of Aluminum in prominent 
sets. The specifications call 
for Aluminum Box Shields 



> 



to insure amplification, tone 
quality, sensitivity and selec- 
tivity. 

The standard "knock-down" 
ALUMINUM BOX SHIELDS 
5"x9"x6" are adaptable to 
many hook-ups. 

Write for new booklet, "Alu- 
minum for Radio," telling of 
the advantages of Alumi- 
num in Radio apparatus. 



ALUMINUM COMPANY OF AMERICA 

2464 Oliver Building, Pittsburgh, Pa. 

Offices in 18 Principal American Cities 



ALUMINUM IN EVERY COMMERCIAL FORM 



54 



RADIO BROADCAST ADVERTISER 




Not Regenerative! Not Tuned 



A. C. Tube Models 



R. G. S. "Octa-Monic" 
A-C Tube Kit 

including instructions and blue-prints; all 
necessary apparatus, ready to build, 
$119.60 







R. G. S. "Octa-Monic" 
A-C Tube Chassis 

Completely assembled according to latest 
laboratory methods, (carefully tested and 
selected heavy duty urire, lamp socket 
connections, cable, Power (A-C) Trans- 
former, etc., etc.,) with instructions and 
blue-prints for installation, ready to plug 
in your lamp socket and operate, $129.60 

R. G. S. "Octa-Monic" 
A-C Tube Receiver 

housed in an attractive, partitioned, toal- 
nut table cabinet, $149.60 

NOTE: All models of the R. G.S. 
"Octa-Monic" have been adapt- 
ed to the Cunningham A-C and 
Power Tubes (Four (4) CX 326, one 
(/) C 327, and one (1) CX 371.) 
The "B" Battery Eliminator and 
the Cunningham Tubes are not 
included in the following prices. 
This eliminates an unnecessary 
expenditure on your part be- 
cause the A-C Tube models of 
the R. G. S. "Octa-Monic" have 
been designed to operate satis- 
factorily with any good "B" 
Eliminator. It is recommended 
if your "B" Eliminator has no 
"C" battery tap, that you use 
the regular 40 volts of C battery. 

Price Notice 

Above prices do not include Cunningham 
A-C and Power Tubes nor the "B" Bat- 
tery Eliminator. All A-C models mill 
operate on any good eliminator. This, 
there/ore permits the use of your own "B" 
Battery Eliminator, thereby representing 
a very distinct saving to you. 




The fundamentally new R. G. S. "Octa-Monic" Receiver developed by David 
Grimes is one of the four great radio developments of the past 10 years. The 
R. G. S. "Octa-Monic" principles are fully as important and represent as basic 
a contribution to the Radio Art as did any of the discoveries of DeForest, Arm- 
strong, Alexanderson, etc., etc. 

These new and revolutionary principles of tuning, or the radio frequency end 
of the R. G.S. "Octa-Monic," produce results not only superior but, these 
principles of tuning place this Receiver far in advance of any receiver developed 
to date. The R. G. S. "Octa-Monic" is fundamental and is as radically new as 
was the Super-Heterodyne. 

These highly efficient principles employed in the new R. G. S. "Octa-Monic" 
cover not only the tuning or radio frequency end of this receiver but they cover 
the amplification end as well. The R. G. S. "Octa-Monic" amplifier (Power 
tube in the last stage,) gives, unquestionably, as perfect reproduction as it is 
possible to buy, regardless of cost. 

The^R. G. S. "Octa-Monic" comes to you more heavily endorsed by able au- 
thorities than any other receiver ever presented to the Radio Public. The editor 
of one of the most important radio publications in America said that it was the 
only receiver he had ever seen in his career as an editor to which the terms "new 
and revolutionary" could be applied in good faith. 

Selectivity superior to the super-heterodyne without cutting side bands. Selectivity enough to 
eliminate the heterodyne squeals of local stations, operating on a higher octave; selectivity that is 
equal over the whole dial without being at all critical at any point; selectivity enough to separate 
with ease the local jumble of Metropolitan (New York City, Chicago, San Francisco, etc.) stations; 
selectivity enough to give five (5) degrees of silence between stations WEAF and WNYC in a lo- 
cation 200 yards away from WNYC. 

Selectivity positive enough to make use of vernier control unnecessary. 

Sensitivity or Distance-Getting Ability. Can work right down to static level. This in- 
sures trans-continental or trans-oceanic reception on favorable occasions. 

Volume sufficient to fill a hall that will seat 3500. 

Tonal Quality that is as nearly perfect as development in the Radio Art will permit-. 

Straight Line Audio Amplification. 

Stability Margin of 800 ohms. The average receiver has a stability margin of from 6 to 
20 ohms. This high stability margin of the R. G. S. "Octa-Monic" eliminates any possibilities of 
howling from poor batteries or "motor-boating" from eliminators. Batteries registering as low as 
10 volts will deliver a clear tone, free from howling, in this receiver. 

Straight Line Radio Amplification insuring reception at all broadcast wavelengths. 

Straight Line Volume Control that makes distorting of tone impossible. 

DEALERS: Write for Complete Merchandizing Proposals 



BUILT FOR MODERN 




BROADCAST CONDITIONS 



RADIO BROADCAST ADVERTISER 



jt(j(yn& 




Automatic Wavetrap for prevention of heterodyning and whistling resulting from stations 
operating on one-half wave-length or on first octave beat. 
Automatic Filament Control. 
Employs 135 Volts or 180 Volts. Draws 22 mils. 

Each R. G. S. "Octa-Monic" is carefully tested with scientific apparatus and under actual broad- 
casting conditions before it leaves the laboratories; while every piece of apparatus is just as thor- 
oughly tested before it is built into this receiver. 

The R. G. S. "Octa-Monic" is a closely co-ordinated Receiver built of quality apparatus. Careful 
tests are the basis for the choice of each piece of apparatus, tests that not only determine the merits 
of each individual part, but more importantly its relation to the whole receiver. 

Standard Cunningham tubes (5 CXjoi-A's and i CXjyi, Power tube in last stage) and Western 
Electric Cone are recommended for best results. 

The R. G. S. "Octa-Monic" is highly attractive in appearance. It is built on five-ply, specially 
shellaced sub-panel (20" x 9") to which is mounted a beautiful walnut finished, standard size 
panel (7" x 21") that will fit any good cabinet or fine console 7" x ai". The panel and drum 
escutcheons are trimmed in dull bronze. 

You will find your R. G. S. "Octa-Monic" mighty easy to operate. 

There are but two drums with vernier adjustments and two control knobs, one of which is an or- 
dinary volume control and filament switch, the nearest approach to tuning efficiency, possible. 
Stations actually "click" or "tumble-in" as you slowly revolve your drums. 

The customary need of wooden screw-drivers or involved balancing devices is entirely removed 
in the R. G. S. "Octa-Monic." Major or minor adjustments are unnecessary . The R. G. S. "Octa- 
Monic" is free from ordinary service. Tuning condensers are the only moving parts, and as a conse- 
quence, there are no fussy mechanisms, either mechanical or electrical, to get out of order. 

The R. G. S. "Octa-Monic" operates satisfactorily on either a good "B" battery eliminator or 
batteries without "motor-boating" or howling. 

Orders cannot be accepted for individual pieces of apparatus or blueprints. 

The R. G. S. "Four" employing the Inverse Duplex System (i) R. G. S. "Four" Kit, all parts, com- 
plete instructions, $74.40. (2) Chassis, assembled according to latest laboratory methods, $84.40. 

All prices slightly higher west of Denver. Canadian and Export prices on request. 

Go to your dealer to-day and insist on a demonstration. If he hasn't stocked the R. G. S. "Octa- 
Monic" yet, tear off and mail to us the attached coupon with the required information. Every effort 
will be made to arrange a demonstration for you. 

Arrange for that demonstration now because you have a real radio thrill waiting for you. In the 
R. G. S. "Octa-Monic" you will hear radio at its best. And when you hear the R. G. S. "Octa- 
Monic" you will know why it is: "The Synonym of Performance." 

All models of the R. G. S. "Octa-Monic" and the R. G. S. "Four" are fully protected by 
Grimes Patents issued and pending. 
'Trade Marl{ Registered. 

DEALERS: Write for Complete Merchandizing Proposals 

R-G-S Manfg. Co., Inc. 



Staten Island 



New York 



Battery or "B" Elim- 
inator Models 

R. G. S. "Octa-Monic" Kit 

of parts including all required apparatus, 
complete instructions and blue-prints, 
ready to build, $84.60. 




R. G. S. "Octa-Monic" Chassis 

complete!} assembled according to latest 
laboratory methods, (closely co-ordinated 
and specially designed apparatus, eight 
foot Da Hery cable, etc., etc.) with com- 
plete operational instructions, ready to 
operate, $89.60. 

R. G. S. "Octa-Monic" Receiver 

housed in an attractive, u>ell-designed,uial- 
nut table cabinet, $104.60 

R. G. S. "Octa-Monic" 
Tuning Kit 

including all necessary apparatus and com- 
plete blue-prints and instructions, $63.60 

R. G. S. "Octa-Monic" 
Tuning Chassis 

completely assembled according to latest 
laboratory methods ttuth complete instruc- 
tions and ready to unre to your favorite 
amplifier, $66.60 

Price Note 

The apparatus required to build the rod- 
ically new and fundamental R. G. S. 
Octa-Monic actually lists at oner SIOO.QO. 



R. G. S. MANFG. CO., Inc. 
Staten Island, New York 

Gentlemen: 

Please arrange with my dealer, whose address I have printed 
below, for a demonstration of the new and'revolutionary R. G. S. 
"Octa-Monic". I am much interested in this receiver but this 
request for a demonstration and literature, you understand, en- 
tails no obligation on my part. 



My Name 

Street 

City or State 

My Dealer's Name 
His Address 




BUILT FOR MODERN 




BROADCAST CONDITIONS 




56 



RADIO BROADCAST ADVERTISER 




Kept 
Cool 

Li\e the Best 
Airplane Motors 

TRUVOLT 

An All'Wire Variable 
Voltage Control 

Here is the finest voltage con' 
trol you can possibly buy for 
your power devices! Its spec- 
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gives greater radiation area and 
keeps it cool like an air-cooled 
engine. This prevents dete- 
rioration and assures permanent 
accuracy with long life. 

Resistance made entirely of 
nichrome wire with very low 
temperature coefficient and ex- 
posed directly to air -heat not 
held in by enamel coverings as 
in other resistances. Permits 
potentiometer control and 
gives positive metallic contact 
at all times with 30 exact read- 
ings of resistance. 



Type 

T-5 

T-io 

T'20 

T-50 
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T'200 

1-250 
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Ohms 
Resistance 

O to 500 
O to I.OOO 
O to 2.OOO 

o to 5,000 

O to IO,OOO 
O to 2O,OOO 

o to 25,000 
o to 50,000 



Milliamperes 
Current 

224 
158 
112 

71 
50 

35 
32 
22.5 



Eight stock types with resist- 
ances up to 50,000 ohms. All 
rated at 25 watts. 

List $3.50 each 

Also full line of fixed wire 
resistances. 

Write for free circular 

"This Is An 
Eliminator Year" 

Dept. 14A 

175 Varick Street 

New York 



ELECT RAD 



The Radio Broadcast 



SHEETS 



THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this 
magazine and have appeared since our June, 1926, issue. They cover a wide range 
of information of value to the experimenter and to the technical radio man. It is not our 
purpose always to include new information but to present concise and accurate facts in 
the most convenient form. The sheets are arranged so that they may be cut from the 
magazine and preserved for constant reference, and we suggest that each sheet be cut out 
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should 
be arranged in numerical order. An index appears twice a year dealing with the sheets 
published during that year. The first index appeared on sheets Nos. 47 and 48, in No- 
vember, 1926. In July, an index to all sheets appearing since that time was printed. 

The June, October, November, and December, 1926, issues are out of print. A com- 
plete set of Sheets, Nos. I to 88, can be secured from the Circulation Department, 
Doubleday, Page & Company, Garden City, New York, for Ji.oo. Some readers have 
asked what provision is made to rectify possible errors in these Sheets. In the unfor- 
tunate event that any such errors do appear, a new Laboratory Sheet with the old 
number will appear. 

THE EDITOR. 



No. 137 RADIO BROADCAST Laboratory Information Sheet November, 192? 

Operating Vacuum Tubes in Parallel 



METHODS AND RESULTS 

TT IS sometimes desirable to operate several tubes 
- 1 in parallel in order to obtain a greater power 
output, and it is of interest to know how efficiently 
this may be done. 

If two tubes are to be used in parallel in the 
output of an audio amplifier the two sockets are 
wired so that the grid of one tube connects to the 
grid of the other tube and the two plates connect 
together. The two filaments are also connected 
together. The result is that from these two tubes 
we will have only four leads one from the grids, 
another from the plates, and two others from the 
filaments. 

The amplification constant of the combination 
will be equal to the constant of a single tube, pro- 
vided both of the tubes have the same constant. If 
one of the tubes had a low amplification constant 
and the other a high constant the resultant amplifi- 
cation constant of the two would be equal to the 
arithmetic mean. If the amplification constant of 
one tube is six and the other four, the resultant 
amplification constant will be five. 

The resultant plate impedance will be equal to 
one half the impedance of a single tube, and if unlike 
tubes are used, the total impedance can be calcu- 
lated by the simple laws governing resistances in 



parallel. The combined impedance can be stated as 
follows: 

Imped, of one tube X Imped, of other tube 
Imped, of one tube + Imped, of other tube 

The greatest power output is obtained when the 
two tubes have identical plate impedances and 
amplification constants. Fortunately, however, a 
very large fraction of the total power of the two 
tubes can be obtained even if they differ consider- 
ably. 

To illustrate, two tubes might be connected in 
parallel, the amplification constants of which are 
in a ratio of 2 to 1, and the plate impedances of 
which are equal, and from the combination we could 
obtain 90 per cent, as much power as could be ob- 
tained if the tubes were operated in separate cir- 
cuits. If, with equal amplification constants, the 
plate impedances are in a ratio of 2 to 1, the total 
power will be about 90 per cent, of the maximum 
possible value. It is evident, therefore, that the 
total power will not be decreased by any great 
amount even if tubes quite widely differing in 
characteristics are used. From two perfectly 
matched tubes, feeding into a load resistance 
equal to their combined plate impedance, we can 
obtain twice as much power as can be obtained from 
a single tube feeding into a load resistance equal to 
its plate impedance. 



No. 138 RADIO BROADCAST Laboratory Information Sheet November, 1927 

The Unit of Capacity 

CALCULATION AND FORMULAS where C = capacity of condenser in microfarads 
K = dielectric constant 
'T'HE capacity of a condenser is stated in terms of A = total area of dielectric between 
1 the quantity of electricity it will hold per volt. plates in square inches 
When a condenser stores a specific quantity of elec- d = thickness of dielectric in inches 
tricity known as a coulomb and there is an elec- Example: 
trical pressure of one volt across its terminals then What is the capacity in microfarads of a con- 
the capacity of the condenser is one "farad." A denser having 2000 plates? The dielectric consists 
condenser must be very large to have a capacity of of paraffined paper 0.002 inch thick. The part of 


Vaseline Ebonite Glass Mica ^a*" Porcelain 


Oiiart? Rpsin shpllar Castor Olive Petroleum 
Quartz h leilac Qi , QJ, oa 


2.0 3.0 7.0 6.0 2.5 4.0 


4.5 2.5 3.5 5.0 3.0 2.0 


a farad and therefore a millionth part of a farad 
has been adopted as the practical unit and it is 
called the "microfarad," meaning one-millionth of 
a farad. Capacities smaller than one microfarad can 
be expressed in micro-microfarads, corresponding to 
a millionth of a microfarad. 
The capacity of a condenser may be computed 
from the general equation -. 

_ 2250 AK 


each sheet of dielectric actually between the plates 
has an area of 6.3" x 8". 
From the table in this sheet it will be seen that the 
constant of the dielectric is 2.5. 
The total area, A. of the dielectric is: 
A = 6.3 x 8 x 2000 
= 100.000 square inches, approximately 
Therefore 
_ 2250 x 100,000 X 2.5 


10' x 0.002 
= 28.1 microfarads 


10'd 



RADIO BROADCAST ADVERTISER 



57 



. . . Modern 




Radio is better \vith Battery Power 



NOT because they are new 
in themselves, but because 
they make possible modern 
perfection of radio recep- 
tion, batteries are the mod- 
ern source of radio power. 
Today's radio sets were 
produced not merely to 
make something new, but 
to give you new enjoyment. 
That they will do. New plea- 
sures await you; more espe- 
cially if you use Battery 
Power. Never were receiv- 
ers so sensitive, loud-speak- 
ers so faithful; never has 
the need been so imperative 
for pure DC, Direct Current, 
that batteries provide. You 
must operate your set with 



current that is smooth, 
uniform, steady. Only such 
current is noiseless, free 
from disturbing sounds and 
false tonal effects. And 
only from batteries can such 
current be had. 

So batteries are needful 
if you would bring to your 
home the best that radio 
has to offer. Choose the 
Eveready Layerbilt "B" 
Battery No. 486, modern in 
construction, developed 
exclusively by Eveready to 
bring new life and vigor to 
an old principle actually 
the best and longest-lasting 
Eveready Battery ever built. 
It gives you Battery Power 




Here if the Ereready 
Laytrbilt"B" Battery No. 
486, Eveready's longest- 
lasting provider of Bat' 
tary Power. 



for such a long time that 
you will find the cost and 
effort of infrequent replace- 
ment small indeed beside 
the modern perfection of 
reception that Battery 
Power makes possible. 

NATIONAL CARBON CO., INC. 
New York |M B l la l San Francisco 

Unit of Union Carbide and Carbon Corporation 

Tuesday night is Eveready Hour Night 
9 P. M., Eastern Standard Time 

WEAF-AW York WOC-DotiMiporl 

WJAR Providence WCCO { ^" nnea P"* 
WEEI Boston \ Si. Paul 

WFI-Philadrlphia KSD-S. Louis 

WGR-Ouffalo WDAF-Kon.a. City 

WC\f.-Pittsburfh WRG-R'ashington 

WSAI-CmcinnalJ WGVSefieneclady 

WTAM-Cfftic/ond WHAS-ioui(H 

WWJ-Delroit WSB Atlanta 

WGfi-Chicago WSM-ffashville 
WVtC-Memphis 

Pacific Coast Stations 
9 P. M., Pacific Standard Time 

KPO KGO .San Francisco KFJ Los Angelfs 

KFOA-KOMO-SeaHjo KCW-Porf/onrf 




Radio Batteries 

\rthey last longer 



The 



air 



i s 



full of things you shouldn't 



miss 



58 



RADIO BROADCAST ADVERTISER 



CME 

^Celatsite 
lattery Cable 

A rayon-covered cable of 5, 
6, 7, 8 or 9 vari-colored 
Flexible Celatsite wires for 
connecting batteries or 
eliminator to set. Plainly 
tabbed; easy to connect. 
Gives set an orderly ap- 
pearance. 

Stranded Enameled 

Antenna 

Best outdoor an- 
tenna you can 
buy. Seven 
strands of enam- 
eled copper wire. 

Presents maximum 




surface for reception, 
resists corrosion ; this greatly 
improves thesignal. Outside 
diameters equal to sizes 14 
and 16. (We also offer solid 
and stranded bare, and 
stranded tinned antenna.) 

Loop Antenna Wire 

Sixty strands of No. 38 bare 
copper wire for flexibility, 5 
strands of No. 36 phosphor 
bronze to prevent stretching. 

Green or brown silk covering; best 

loop wire possible to make. 

Flexible Celatsite 
for sub-panel wiring 
A cable of fine, tinned 
copper wires with non- 
inflammable Celatsite in- 
sulation. Ideal for 
sub-panel or 
point - to - point 
wiring. Strips 
easily, solders readily. Nine beauti- 
ful colors; told only in 25 ft* coilt, 
in cartonm colored to match content*. 

Acme 

Celatsite Wire 
Tinned copper bus bar hook- 
up wire with non-inflam- 
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easily, solders readily, won't 
crack at bends. Sizes 14, 16, 
18, 19; 30 inch lengths. 

Spaghetti Tubing 
Oil, moisture, acid proof; highly 
dielectric used by leading engi- 
neers. Nine colors, for wire sizes 12 
to 18; 30 inch lengths. (We also 
make tinned bus bar, round and 
square, in 2 and 2} ft. lengths.) 

Send for folder 

THE ACME WIRE CO., Dept. B 
New Haven, Conn. 




ACM 



IRE 



MAKES BETTER RADIO. 1 



No. 139 



RADIO BROADCAST Laboratory Information Sheet November, 1927 



Inductive Reactance 



HOW IT IS CALCULATED 

TF AN inductance coil is connected in series with an 
* a. c. ammeter to a source of alternating current, 
a certain amount of current will flow in. the circuit, 
depending upon the size of the coil and the fre- 
quency of the current. If the voltage of the source is 
divided by the current, the quotient will be the 
"reactance" of the coil in ohms. For example, if 
the frequency of the current being supplied by the 
source of potential was 60 cycles and the voltage was 
110 volts and the coil had an inductance of 1.0 
henry, we would find that 0.292 amperes of current 
would flow through the circuit. Then 110 volts 
divided by 0.292 gives 377, which is the reactance in 
ohms at 60 cycles of a coil with an inductance of 
1 .0 henry. The reactance of a coil depends upon its 
inductance and upon the frequency of the current. 
It can be calculated by means of the following 
formula : 

Reactance = 6.28 FL 
where F = the frequency of the current in cycles 



per second, and L = the inductance of the coil in 
henries. 

In many calculations it is necessary to know the 
reactance of some particular coil at some frequency 
and for this reason on Laboratory Sheet No. 140 is 
given a table of reactance for inductance coils be- 
tween 0.01 and 100 henries at frequencies from 60 
to 100,000 cycles. From the formula given herewith 
it is evident that the reactance of a coil is directly 
proportional to the inductance of the coil and also 
directly proportional to the frequency. Doubling the 
size of the coil gives twice the reactance and twice 
the reactance is also obtained if the frequency is 
doubled. If these two factors are remembered it is a 
simple matter to calculate mentally the reactance 
of any coil not given in the table on Laboratory 
Sheet No. 140. For example a 10-henry coil has one 
third the reactance of a 30-henry coil at, say, 100 
cycles. Since the reactance of a 10-henry coil at 
100 cycles is 6280 ohms, it follows that the reactance 
of a 30-henry coil at the same frequency must be 
18,840 ohms. 



No. 140 RADIO BROADCAST Laboratory Information Sheet November, 1927 


Coil Reactance 


COIL INDUCTANCE 
IN HENRIES 


REACTANCE IN OHMS AT VARIOUS FREQUENCIES 


60 


100 


250 


500 


1000 


10,000 


100.000 


0.01 


3.77 


6.28 


15.7 


31.4 


62.8 


628 


6,280 


0.05 


18.8 


31.4 


78.5 


157 


314 


3,140 


31,400 


0.1 


37.7 


62.8 


157 


314 


628 


6,280 


62,800 


0.5 


188.5 


314 


785 


1,570 


3,140 


31,400 


314,000 


1.0 


377 


628 


1,570 


3,140 


6,280 


62,800 


628,000 


2.0 


754 


1,256 


3,140 


6,280 


12,560 


125,600 


1,256,000 


5.0 


,885 


3,140 


7,850 


15,700 


31,400 


314,000 


3,140,000 


10.0 


3,770 


6,280 


15,700 


31.400 


62,800 


628,000 


6,280,000 


20.0 


7,540 


12,360 


31,400 


62,800 


123,600 


1 ,236,000 


12,360,000 


30.0 


11,310 


18,840 


47,200 


94,200 


188,400 


1,884,000 


18,840.000 


40.0 


15,080 


24,720 


61.800 


123,600 


247,200 


2,472,000 


24,720.000 


50.0 


18,850 


31,400 


78,500 


157,000 


314,000 


3,140,000 


31,400,000 


100.0 


37,700 


62,800 


157,000 


314,000 


628,000 


6,280,000 


62,800,000 


This table shows how the reactance of various inductance coils varies with different frequencies. Labor- 
atory Sheet No. 139 explains what inductive reactance is and upon what it depends. 



No. 141 RADIO BROADCAST Laboratory 


Information Sheet November, 1927 


A. C. Tube 


Data 




"HEATER" AND FILAMENT TYPES 


that heavv wire be used. Determine the total cur- 


rent required by all the tubes and table No. 1 below 
(~)N THIS Laboratory Sheet are given data on will tell you what size of wire to use. 


W the new a. c. tubes, type 


UY-227 (c-327 


and 


TABLE No. 1 




type ux-226 (cx-326). The fo 


rmer tube is < 


>f the 


Size 


Current 


heater type whereas the latter is of the a. c. filament 
type. The heater tube requires a special five-prong 
socket whereas the type 26 may be used with any 


(B & S Gauge) 
12 20 
14 11 


amperes 
amperes 


standard socket. The filament 


voltage and current 


16 6 


amperes 


of the type 27 are 2.5 volts a 


id 1.75 amper 


es re- 


18 3 


amperes 


spectively. The type 26 requires a filament voltage 
of 1 .5 volts and the filament current is 1 .05 amperes. 


20 1 


5 amperes 


The filament current of these tubes is quite large, Table No. 2 on this sheet gives the characteristics 
especially so in a multi-tube receiver, and for this of these tubes under various conditions of plate and 


reason it is essential in wiring 


the filament 


leads grid voltage. 






TABLE No. 


2 
















UNDISTORTED 


TYPE 
OF TUBE 


PLATE 
VOLTAGE 


NEGATIVE 
GRID 
VOLTAGE 


PLATE 
CURRENT 


PLATE 
IMPEDANCE 


MUTUAL 
CONDUCTANCE 


POWER 
OUTPUT IN 
WATTS 


UY-227 


90 


5 


3 


11,300 


725 


0.020 


& 


135 


9 


5 


10,000 


820 


0.055 


c-327 


180 


13.5 


6 


9,400 


870 


0.140 


ux-226 


90 


6 


3.7 


9,400 


875 


0.020 


& 


135 


9 


6 


7,400 


1100 


0.070 


cx-326 


180 


13.5 


7.5 


7,000 


1170 


0.160 





RADIO BROADCAST ADVERTISER 



59 



Dalkite has pioneered 

but not at public expense 

Tit 




" A" Contains no bat- 
/\ fcry.Thesameas 
Balkice "AB "but for the "A" circuit only. 
Not a battery and charger but a perfected 
light socket "A" power supply. One of the 
most remarkable developments in the 
entire radio field. Price $32.50. 




Ballrite "B" 9 /?* ltmgest 

JJcUKllC U lived devices in 
radio. The accepted tried and proved light 
socket "B" power supply. The first Balkite 
"B," after 5 years, is still rendering satis- 
factory service. Over3oo,oooinuse. Three 
models: "B"-W, 67-90 volts, $22.50; 
"B"-i35,* 135 volts, #32.50; "B"-i8o, 
180 volts, $39.50. Balkite now costs no 
more than the ordinary "B" eliminator. 




Balkite Chargers 

Standard for "A" batteries. Noiseless. Can 
be used during reception. Prices drastically 
reduced. Model "J,"* rates 2. 5 and .5 am- 
peres, for both rapid and trickle charging, 
$17.50. Model "N"* Trickle Charger, 
rate .5 and .8 amperes, $9.50. Model "K" 
Trickle Charger, $7.50. 

* Special models for 25-40 cycles at 
slightly higher prices 

Prices are higher West of the 
Rockies and in Canada 



n 
in 



alone remains in its original form; all 
others have either been radically re-, 
vised in principle or completely with- 



power have been made 

I D // oecause the hrst Balkite "J3," pur- 

Oy >alk.ite Firstnoiselessbat- chased 5 years ago, is still in use and 

tery charging. Then successful light wil1 be for X ears to come, 

socket "B" power. Then trickle charg- Because to your radio dealer Bal- 



in 
al 



And today, most important of kite is a synonym for quality. 



Balkite "AB," a complete unit 
containing no battery in any form, 
supplying both "A" and "B" power 
directly from the light socket, oper- 
ating only while the set is in use. 

This pioneering has been impor- 
tant. Yet alone it would never have 
made Balkite one of the best known 
names in radio. Balkite is today the 
established leader because of Balkite 
performance at 
the hands of its 
owners. 

Because with 
2,000,000 units 
in the field Bal- 
kite has a record 
of long life and 
freedom from 
trouble seldom 
equalled in any 
industry. 

Because of 
the first 16 light 
socket "B" 
power supplies 
put on the mar- 
ket, Balkite "B" 




Balkite " AB 



Contains no battery. 

A complete unit, replacing both "A" and "B" batteries 
and supplying radio current directly from the light 
socket. Containsnobatteryinanyform. Operatesonly 
while the set is in use. Two models: "AB" 6-135, '135 
volts"B"current,$59.5o;"AB"6-i8o,i8ovolts,$67.5O. 



Because the electrolytic rectification 
developed and used by Balkite is so 
reliable that today it is standard on 
the signal systems of most American 
as well as European and Oriental 
railroads. 

Because Balkite is permanent 
equipment. Balkite has pioneered 
but not at the expense of the public. 
Today, whatever type of set you 
own, whatever 
type of power 
equipment you 
want (with bat- 
teries or with- 
out), whatever 
you want to pay 
for it, Balkite 
has it. And pro- 
duction is so 
enormous that 
prices are aston- 
ishingly low. 

Your dealer 
will recommend 
the Balkite equip- 
ment you need 
for your set. 



FANSTEEL PRODUCTS COMPANY, INC., NORTH CHICAGO, ILLINOIS 



Licensees for Germany: 

Siemens K Halske, A. G. Wernerwerk M 

Siemensscadc, Berlin 



Sole Licensees in the United Kingdom: 
Messrs. Radio Accessories Ltd., 9-13 Hythe Rd. 
Willesden, London, N. W. 10 



r"" M-EEL 

Balkite 




Tower Units 



60 



RADIO BROADCAST ADVERTISER 



K4RA5 



Parts Make the 2 Dial Karas 

Equamatic the World's Best 

5-Tube Receiver 




"V"OU have r^ad and 
* heard much about 
the new 2-Dial Karas 
Kqiiamatic the -VTube 
Receiver that is the talk 



of its perfect neutrali- 
zation and its Cinn- 
pletely balanced opera- 
tion. The results you 
may expect from this re- 



natural 



Ul 



Phenomenal, and tlie 2- 
Dial Equamatic delivers 
ei-ett more than you ex- 
pect. The use of Karas 
Farts insures this. These 
parts are essential to the 
perfect operation of the 
-'-Dial Kquamatic, for 
the receiver is built 
md them. Some of 




The NEW Karas Output 
Filter, Price #8.00 



The NEW Karas Type 28 "' fain 119 art8 arfl . 

Audio Transformer J n d w J ^ut. ^ , 

Price, {(8.00 a ll the necrssary Karaa 

I'arts elsewhere in this 

advertisement. 

A Marvelous Purity of Tone 

'T'HE 2-Dial Karas 
-* Equamatic possesses a 
marvelous purity of 
tone, due to Its utiliza- 
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Tjpe 28 I impregnated 
Audio Transformers 
the new Karas Trans- 
fer men inclosed in 
spun-sealed lifetime 

steel-clad rases. The new 
Karaa Output Filter also 
aids in building up a 
clear, sweet tone for the 
2-Dial Fquamatic. This 
receiver owes much of 
Its extremely efficient 
operation to the use of 
the new Karas S- F. I,. 
Variable Condensers, 
and Karas Micrometrlc 
Dials aid in giving the 
et 1-1000 of an Inch 
tuning. The heart of the 
Equamatic of course is 
the Kara* Equamatic In- 
ductance Coils, with their variable primaries and ad- 
justable secondaries which enable the energy transfer be- 
tween these two coils to be automatically and continuously 
maintained at every wave length setting of the dials. 

Easy to Build this Receiver 

YOU can easily build 
this 2-Dial Karas 
Equa mati c 5-Tube H e- 
ceiver In a short time by 
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necessary Karas and 
other parts. We supply 
FREE complete blue 
prints and instructions 
for huildlne. The Karas 
Parts you will need are 
as follows: 2 Type 28 
Karas Audio Transform- 
ers, each $8; 1 Karas 
Output Filter, *8; 3 New 
Karas Type 17 Variable 
Condensers, each *!i.25; 
3 Karas Equamatic Coils, 
ea,-h $4; 2 Karaa Mfcro- 

The NEW Karas S.F.L. metric Dials, each $3.60; 

Condenser with Removable J t J r t b ^\ B iVrj 

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Have You Heard the Knickerbocker 4-- 
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nn 7 
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.OOO5 mfd. 55.50 




_ _ _ _ _ . Coupon ~~ ^ 

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n2-T)ial Karas Equa- 
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DKnii-kerhorlm-4 
The Wonder Set 



City 



No, 142 RADIO BROADCAST Laboratory Information Sheet November, 1927 

Obtaining Various Voltages from a B-Power Unit 

VALUES AND CURRENT-CARRYING CAPACITY the total drain from the 90-volt tap is 10 milliam- 

IT IS comparatively simple to calculate the resis- peres. Then the total current flowing through Ri 
tance values required in the output circuit of a will be equal to 10 plus 1 plus 3, or 14 milliamperes. 
B-power unit in order to obtain any specific vol- If the maximum voltage available from the power 
tages. This Laboratory Sheet will explain how to unit is 180 and the voltage at terminal No. 2 is to 
calculate the values of these resistances. be 90, it follows that the voltage drop across Ri 

Consider the fundamental output circuit of a must be 90. Ninety volts divided by 0.014 amperes 
B-power unit as illustrated in the sketch. The dia- gives 6400 ohms as the value of Ri. 
gram of the rectifier and filter has been omitted *^_ _.. - 

since they play no important part in the calculation 
of resistance values. Suppose tap No. 1 is to be 45 
volts and is to be used to operate a detector tube. 
We will assume that the loss current through Rs is 3 
milliamperes, or 0.003 amperes. This is an average 
figure for the loss current and can generally be used 
in this type of calculation. If the voltage at tap 
No. 1 is to be 45, then the voltage drop across re- 
sistance Rs must be 45. The resistance of Rs will 
be equal to the voltage across it divided by the 
current through it or, in this case, 45 divided by 
0.003, which gives 15,000 ohms as the value of R 3 . 
The voltage at tap No. 2 is to be 90. Since the volt- 
age drop across R-> is 45, it follows that the voltage 
drop across Ra will also be 45 in order to make the 
total voltage between the negative B and tap No. 2 
equal to 90. The current (lowing through the resis- 
tance Ra will be equal to the loss current at 3 milli- 
amperes plus the current drawn by the detector 
tube, which is 1 milliampere. Therefore the value 
of resistance R2 will be equal to the voltage across 
it, 45, divided by the current through it, which is 
0.003 plus 0.001, or a total of 0.004 amperes. This 
gives a value of 11,250 ohms for R 2 . Suppose that 



Dm 
ter 


1 
o 
1 


Rj 


** 2 


I* 



B- 

Resistance units for B power units are usually 
rated in watts and it is essential that the resistances 
used be capable of carrying the necessary load 
without overheating. The load in watts being han- 
dled by a resistance can be determined by multiply- 
ing the resistance in ohms by the square of the 
current in amperes. In this particular example: 

Watts through Rj = 15000 X 0.003' 
= 0.135 watts 

Watts through R 2 = 11250 X 0.004' 
= 0.18 watts 

Watts through Ri = 6400 X 0.014 2 
= 1.25 watts 



No. 143 RADIO BROADCAST Laboratory Information Sheet November, 1927 

Solenoid Coil Data 

UNITS FOR THE BROADCAST BAND mfd. variable condensers. The wavelength range of 
the coil will be approximately 200 to 550 meters. 
THIS Laboratory Sheet gives the data necessary The coils may be wound on hard rubber or bakelite 
to wind the secondaries of solenoid type coils tubing, or some type of self-supported winding may 
for use with 0.0005-mfd., 0.00035-mfd., or 0.00025- be used. 


DIAMETER OF 
TUBE IN INCHES 


SIZE OF WIRE 


NUMBER OF TURNS OF D.C.C. WIRE REWIRED WITH VARIOUS 
SIZES OF TUNING CONDENSERS 


0.0005 mfd. 


0.00035 mfd. 


0.00025 mfd. 


31 


28 
26 
24 
22 
20 


28 
31 
34 
38 
42 


38 
42 
46 
50 
55 


50 
54 
58 
64 
72 


3 


28 
26 
24 
22 
20 


35 

39 
43 
47 
51 


48 
52 
56 
61 
67 


62 
67 
73 
81 
88 


21 


28 
26 
24 
22 
20 


42 
45 
48 
51 
53 


54 
58 
63 
70 

78 


63 
73 
80 
90 

98 





144 RADIO BROADCAST Laboratory Information Sheet November, 1927 



The Transmission Unit 



CORRECTION OF LABORATORY SHEET NO. 114 

TWO errors occurred in LABORATORY SHEET No. 
114 published in the August, 1927, RADIO 
BROADCAST. In the last line in the first column, the 
word "natural" should be changed to read "com- 
mon," and in the first line in the second column, the 
same change should be made. 

The chart on this sheet makes it possible to deter- 
mine easily the number of telephone transmission 
units if the current or voltage ratio is known. For 
example, from the curve it is evident that if two 
voltages or two currents are in a ratio of 5, then the 
TU difference between them is 14. If we are dealing 
with powers rather than currents or voltages, it is 
merely necessary to divide the number of TU ob- 
tained from the curve by 2 in order to determine 
the TU difference of any two powers. For example, 
two powers in the ratio of 8 to 1 have a TU differ- 
ence of 9. To determine this value we look up the 
number of TU corresponding to a ratio of 8 which 
gives 18 and then divide by 2. 

To illustrate the use of the curve we might take 
an audio amplifier requiring a tenth of a volt input 
to produce three volts at the output. If we wanted 
to know the overall gain in TU we would divide 
three by 0.1 , which gives 30. This ratio on the curve 
corresponds to a 29.5 TU voltage gain. 





















^* 




















f 

i 


















/ 




















/ 


















/ 


















/ 




















/ 


















/ 




















/ 




















/ 




















J' 


















/ 




















/ 


















/ 


















/ 


















/ 




















/ 


















/ 




















/ 




















/ 














\ 




2 3456 


i 10 20 30 40 60 8010 



CURRENT OR VOLTAGE RATIO 



RADIO BROADCAST ADVERTISER 



61 



>* 



Announcing 

A. C. TUBES 

Alternating Current 

The new M-26 and N-27 tubes are tubes using raw 
A. C. on the Filament or Heater and can be used in 
any set specifying these types. The M-26 is used in 
the radio and audio frequency stages and has 
a standard base. The N-27, of the separate 
heater type is used as a detector or 
amplifier and has a five prong 
base. These tubes will give su- 
perior results and maximum use- 
ful life in any set designed to use 
A. C. tubes of this type. 



RADIO 
\TUBESr 



Write for particulars 
C. E. MFG. CO., Inc. 

Providence, R. I. U. S. A. 

Largest Plant in the World Making Radio Tubes Eiclvsively 



Heater 



Volt* 



t , 5 



@@ 

"^fo'-Eve, 



RADIO 
TUBES 



CeCo announces a complete kit of tutas for the "Im- 
proved Aristocrat" by Arthur H. L.ynch. Get the kit 
from your dealer and be sure you are right. 



1 Type K, R. K. Amp. - 

1 " H, Spl. Detector - 

2 " G, HiMu Amp. - 
1 " F, Semi Power - 



Price 3.00 
" 2.50 
" 8.00 

" 4.30 
Total for kit *H.50 



;>,. 



Special Radio Frequency types. Demand CeCo. 



62 



RADIO BROADCAST ADVERTISER 










Bradky0hm-E 



PERFECT Vi 



LE RESISTOR 



The graphite disc principle, 
utilized in the construction 
of Bradleyohm-E assures 
noiseless, stepless regulation 
of plate voltage when used 
in B' Eliminator hookups. 

By turning the bakelite knob, 
the plate voltage output of 
the B'Eliminator can be ad' 
justed, without steps or 
jumps, to the precise value 
for maximum volume. That 
is why prominent B'Elimi' 
nator manufacturers have 
adopted Bradleyohm'E. 

Ask your dealer for Brad' 
leyohm'E in the distinctive 
checkered carton. 




firadkpunit-A 

PERFECT FIXED RESISTOR 

This is a solid, molded fixed 
resistor that does not depend 
upon hermetic sealing for 
accuracy. It is not affected 
by temperature or moisture 
and can be soldered with' 
out disturbing its rating. 

For resistance'coupling, 
grid leaks, and other appli' 
cations, ask your dealer for 
Bradleyunit'A in any de' 
sired rating. 





ELECTRIC CONTROLLING APPARATUS 

278GreenfieIdAve. (gD\ Milwaukee, Wit. 

JVWAW.W.W. 



Manufacturers* Booklets 

A Varied List of Books Pertaining to Radio and Allied 
Subjects Obtainable Free With the Accompanying Coupon 



may obtain any of the booklets listed below by us- 
** ing tbe coupon printed on page 64. Order by number only, 

1. FILAMENT CONTROL Problems of filament supply, 
voltage regulation, and effect on various circuits. RADIALL 
COMPANY. 

2. HARD RUBBER PANELS Characteristics and proper- 
ties of hard rubber as used in radio, with suggestions on 
how to "work" it. B. F. GOODRICH RUBBER COMPANY. 

3. TRANSFORMERS A booklet giving data on input and 
output transformers. PACENT ELECTRIC COMPANY. 

4. RESISTANCE-COUPLED AMPLIFIERS A general dis- 
cussion of resistance coupling with curves and circuit dia- 
grams. COLE RADIO MANUFACTURING COMPANY. 

5. CARBORUNDUM IN RADIO A book giving pertinent 
data on the crystal as used for detection, with hook-ups, 
and a section giving information on the use of resistors. 
THE CARBORUNDUM COMPANY. 

6. B-ELIMINATOR CONSTRUCTION Constructional data 
on how to build. AMERICAN ELECTRIC COMPANY. 

7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA- 
TION Circuit diagrams and discussion. ALL-AMERICAN 
RADIO CORPORATION. 

8. RESISTANCE UNITS A data sheet of resistance units 
and their application. WARD-LEONARD ELECTRIC COMPANY. 

9. VOLUME CONTROL A leaflet showing circuits for 
distortionless control of volume. CENTRAL RADIO LABORA- 
TORIES. 

10. VARIABLE RESISTANCE As used in various circuits. 
CENTRAL RADIO LABORATORIES. 

1 1. RESISTANCE COUPLING Resistors and their ap- 

B'ication to audio amplification, with circuit diagrams. 
EjuR PRODUCTS COMPANY. 

12. DISTORTION AND WHAT CAUSES IT Hook-ups of 
resistance-coupled amplifiers with standard circuits. ALLEN- 
BRADLEY COMPANY. 

1 5. B-ELIMINATOR AND POWER AMPLIFIER Instruc- 
tions for assembly and operation using Raytheon tube. 
GENERAL RADIO COMPANY. 

153. B-ELIMINATOR AND POWER AMPLIFIER Instruc- 
tions for assembly and operation using an R. C. A. rectifier. 
GENERAL RADIO COMPANY. 

16. VARIABLE CONDENSERS A description of the func- 
tions and characteristics of variable condensers with curves 
and specifications for their applica'ion to complete receivers. 
ALLEN D. CARDWELL MANUFACTURING COMPANY. 

17. BAKELITE A description of various uses of bakelite 
in radio, its manufacture, and its properties. BAKELITE 
CORPORATION. 

19. POWER SUPPLY A discussion on power supply with 
particular reference to lamp-socket operation. Theory 
and constructional data for building power supply devices. 
ACME APPARATUS COMPANY. 

20. AUDIO AMPLIFICATION A booklet containing data 
on audio amplification together with hints for the construc- 
tor. ALL AMERICAN RADIO CORPORATION. 

21. HIGH-FREQUENCY DRIVER AND SH9RT-WAVE WAVE- 
METER Constructional data and application. BURGESS 
BATTERY COMPANY. 

46. AUDIO-FREQUENCY CHOKES A pamphlet showing 
positions in the circuit where audio-frequency chokes may 
be used. SAMSON ELECTRIC COMPANY. 

47. RADIO-FREQUENCY CHOKES Circuit diagrams il- 
lustrating the use of chokes to keep out radio-frequency 
currents from definite points. SAMSON ELECTRIC COMPANY. 

48. TRANSFORMER AND IMPEDANCE DATA Tables giving 
the mechanical and electrical characteristics of transformers 
and impedances, together with a short description of their 
use in the circuit. SAMSON ELECTRIC COMPANY. 

49. BYPASS CONDENSERS A description of the manu- 
facture of bypass and filter condensers. LESLIE F. MUTER 
COMPANY. 

50. AUDIO MANUAL Fifty questions which are often 
asked regarding audio amplification, and their answers. 
AMERTRAN SALES COMPANY, INCORPORATED. 

51. SHORT-WAVE RECEIVER Constructional data on a 
receiver which, by the substitution of various coils, may be 
made to tune from a frequency of 16,660 kc. (18 meters) to 
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED. 

52. AUDIO QUALITY A booklet dealing with audio-fre- 
quency amplification of various kinds and the application 
to well-known circuits. SILVER-MARSHALL, INCORPORATED. 

56. VARIABLE CONDENSERS A bulletin giving an 
analysis of various condensers together with their charac- 
teristics. GENERAL RADIO COMPANY. 

57. FILTER DATA Facts about the filtering of direct 
current supplied by means of motor-generator outfits used 
with transmitters. ELECTRIC SPECIALTY COMPANY. 

59. RESISTANCE COUPLING^ A booklet giving some 
general information on the subject of radio and the applica- 
tion of resistors to a circuit. DAVEN RADIO CORPORATION. 

60. RESISTORS A pamphlet giving some technical data 
on resistors which are capable of dissipating considerable 
energy; also data on the ordinary resistors used in resistance- 
coupled amplification. THE CRESCENT RADIO SUPPLY 
COMPANY. 

62. RADIO-FREQUENCY AMPLIFICATION Constructional 
details of a five-tube receiver using a special design of radio- 
frequency transformer. CAMFIELD RADIO MFG. COMPANY. 

63. FIVE-TUBE RECEIVER Constructional data on 
building a receiver. AERO PRODUCTS, INCORPORATED. 

64. AMPLIFICATION WITHOUT DISTORTION Data and 
curves illustrating the use of various methods of amplifica- 
tion. ACME APPARATUS COMPANY. 

66. SUPER-HETERODYNE Constructional details of a 
seven-tube set. G. C. EVANS COMPANY. 

70. IMPROVING THE AUDIO AMPLIFIER Data on the 
characteristics of audio transformers, with a circuit diagram 
showing where chokes, resistors, and condensers can be used. 
AMERICAN TRANSFORMER COMPANY. 

72. PLATE SUPPLY SYSTEM A wiring diagram and lay- 
out plan for a plate supply system to be used with a power 
amplifier. Complete directions for wiring are given. AMER- 
TRAN SALES COMPANY, 



80. FIVE-TUBE RECEIVER Data are given for the con- 
struction of a five-tube tuned radio-frequency receiver. 
Complete instructions, list of parts, circuit diagram, and 
template are given. ALL-AMERICAN RADIO CORPORATION. 

81. BETTER TUNING A booklet giving much general in- 
formation on the subject of radio reception with specific il- 
lustrations. Primarily for the non-technical home construc- 
tor. BREMER-TULLY MANUFACTURING COMPANY. 

82. SIX-TUBE RECEIVER A booklet containing photo- 
graphs, instructions, and diagrams for building a six-tube 
shielded receiver. SILVER-MARSHALL, INCORPORATED. 

83. SOCKET POWER DEVICE A list of parts, diagrams, 
and templates for the construction and assembly of socket 
power devices. JEFFERSON ELECTRIC MANUFACTURING COM- 
PANY. 

84. FIVE-TUBE EQUAMATIC Panel layout, circuit dia- 
grams, and instructions for building a five-tube receiver, to- 
gether with data on the operation of tuned radio-frequency 
transformers of special design. KARAS ELECTRIC COMPANY. 

85. FILTER Data on a high-capacity electrolytic con- 
denser used in filter circuits in connection with A socket 
power supply units, are given in a pamphlet. THE ABOX 
COMPANY. 

86. SHORT-WAVE RECEIVER A booklet containing data 
on a short-wave receiver as constructed for experimental 
purposes. THE ALLEN D. CARDWELL MANUFACTURING 
CORPORATION. 

88. SUPER-HETERODYNE CONSTRUCTION A booklet giv- 
ing full instructions, together with a blue print and necessary 
data, for building an eight-tube receiver. THE GEORGE W. 
WALKER COMPANY. 

89. SHORT-WAVE TRANSMITTER Data and blue prints 
are given on the construction of a short-wave transmitter, 
together with operating instructions, methods of keying, and 
other pertinent data. RADIO ENGINEERING LABORATORIES. 

90. IMPEDANCE AMPLIFICATION The theory and practice 
of a special type of dual-impedance audio amplification are 
given. ALDEN MANUFACTURING COMPANY. 

93. B-SOCKET POWER A booklet giving constructional 
details of a socket-power device using either the BH or 3 1 3 
type rectifier. NATIONAL COMPANY, INCORPORATED. 

94. POWER AMPLIFIER Constructional data and wiring 
diagrams of a power amplifier combined with a B-supply 
unit are given. NATIONAL COMPANY, INCORPORATED. 

ipo. A, B, AND C SOCKET-POWER SUPPLY A booklet 
giving data on the construction and operation of a socket- 
power supply using the new high-current rectifier tube. 
THE Q. R. S. Music COMPANY. 

101. USING CHOKES A folder with circuit diagrams of 
the more popular circuits showing where choke coils may 
be placed to produce better results. SAMSON ELECTRIC 
COMPANY. 

ACCESSORIES 

22. A PRIMER OF ELECTRICITY Fundamentals of 
electricity with special reference to the application of dry 
cells to radio and other uses. Constructional data on buzzers, 
automatic switches, alarms, etc. NATIONAL CARBON COM- 
PANY. 

23. AUTOMATIC RELAY CONNECTIONS A data sheet 
showing how a relay may be used to control A and B cir- 
cuits. YAXLEY MANUFACTURING COMPANY. 

25. ELECTROLYTIC RECTIFIER Technical data on a new 
type of rectifier with operating curves. KODEL RADIO 
CORPORATION. 

26. DRY CELLS FOR TRANSMITTERS Actual tests 
given, well illustrated with curves showing exactly what 
may be expected of this type of B power. BURGESS BATTERY 
COMPANY. 

27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS- 
MITTERS Characteristic curves and data on discharge tests. 
BURGESS BATTERY COMPANY. 

28. B BATTERY LIFE Battery life curves with general 
curves on tube characteristics. BURGESS BATTERY COM- 
PANY. 

29. How TO MAKE YOUR SET WORK BETTER A non- 
technical discussion of general radio subjects with hints on 
how reception may be bettered by using the right tubes. 
UNITED RADIO AND ELECTRIC CORPORATION. 

30. TUBE CHARACTERISTICS A data sheet giving con- 
stants of tubes. C. E. MANUFACTURING COMPANY. 

31. FUNCTIONS OF THE LOUD SPEAKER A short, non- 
technical general article on loud speakers. AMPLION COR- 
PORATION OF AMERICA. 

32. METERS FOR RADIO A catalogue of meters used in 
radio, with connecting diagrams. BURTON-ROGERS COM- 
PANY. 

33. SWITCHBOARD AND PORTABLE METERS A booklet 
giving dimensions, specifications, and shunts used with 
various meters. BURTON-ROGERS COMPANY. 

34. COST OF B BATTERIES An interesting discussion 
of the relative merits of various sources of B supply, HART- 
FORD BATTERY MANUFACTURING COMPANY. 

35. STORAGE BATTERY OPERATION An illustrated 
booklet on the care and operation of the storage battery. 
GENERAL LEAD BATTERIES COMPANY. 

36. CHARGING A AND B BATTERIES Various ways of 
connecting up batteries for charging purposes. WESTING- 
HOUSE UNION BATTERY COMPANY. 

37. CHOOSING THE RIGHT RADIO BATTERY Advice on 
what dry cell battery to use; their application to radio, 
with wiring diagrams. NATIONAL CARBON COMPANY. 

53. TUBE REACTIVATOR Information on the care of 
vacuum tubes, with notes on how and when they should be 
reactivated. THE STERLING MANUFACTURING COMPANY. 

54. ARRESTERS Mechanical details and principles of the 
vacuum type of arrester. NATIONAL ELECTRIC SPECIALTY 
COMPANY. 

55. CAPACITY CONNECTOR Description of a new device 
for connecting up the various parts of a receiving set, and 
at the same time providing bypass condensers between the 
leads. KuR7-KASCH COMPANY. 

'Continued on pagt 64} 



RADIO BROADCAST ADVERTISER 



63 




f^ Celestuu^tradivanus 

^me Advanced Hi-Q*Six 

BOTH CUSTOM-BUILT! 




The Hi-Q_ Six the newest advance in radio /our completely 
isolated tuned stages Automatic Variable Coupling symphonic 
amplification. A non-oscillating, super-sensitive receiver that as- 
sures maximum and uniform ampli/ication on all u;ave lengths 
and establishes a totally new standard of tonal qualify. 



S ySUST as Antonio Stradivari gave the 
I 5 priceless Custom'built violin to mu' 
L!o.oS sicians of his day, so does Hammarlund- 
Roberts offer music lovers of our day the 
Custom-built Radio. 

The advanced "Hi-QSix" designed by ten 
of America's leading manufacturers made 
with America's finest parts incorporating 
every modern constructional feature and 
built under your own eyes from plans so com.' 
plete, so exacting and so clear cut that the 
only outcome can be absolute radio perfection. 

In addition to its unprecedented perform' 
ance, the Hi'Q Six offers equally unprecedented 
economy, for by building it yourself you can 
save at least $100.00 over the cost of finest 
factory 'assembled sets. Complete parts in' 
eluding Foundation Unit chassis, panels, with 
all wire and special hardware cost only $95.80. 

The Hi'Q Instruction Book tells the com- 
plete story with text, charts, diagrams and 
photos. Anyone can follow it and build this 
wonderful instrument. Get a copy from your 
dealer or write us direct. Price is 25 cents. 

J^&mmarlund 

R.OQ ELR.TS 

Hi Q* SIX 

HAMMARLUND-ROBERTS, INC. 

1182 Broadway Dept. A New York City 



(Associate ^Manufacturers 



64 



RADIO BROADCAST ADVERTISER 



NEW! 

the 

Two Tube 
Official 

BROWNING- 
DRAKE 
Kit Set 




This new assembly, the two tube 
Official Browning-Drake has been 
designed to be used with any good 
audio transformer system now on the 
market, such as Amertran, Thordar- 
son, etc. The combination gives re- 
markable tone quality and great vol- 
ume. This two tube assembly uses 
only the detector and R. F. tubes. 
Special type T foundation unit 
makes construction easy. The Offi- 
cial Browning-Drake Kit is used. 
Other Browning-Drake Corporation 
products incorporated in the assem- 
bly are the cartridge resistance and 
the neutralizer. 

If your dealer does not carry all of 
the specified parts, send us his name 
and your requirements will be met 
immediately. 

DEALERS: There is profit and 
satisfaction in handling popular 
products. Write or wire TOD A Y 
about the Browning-Drake line 
of parts and the Browning-Drake 
line of factory-built receivers. 

LOOK FOR THIS 




TRADE MARK 

BROWNING-DRAKE CORP. 
Cambridge :: Massachusetts 

BROWNING 
DRAKE 



69. VACUUM TUBES A booklet giving the characteris- 
tics of the various tube types with a short description of 
where they may be used in the circuit. RADIO CORPORA- 
TION OF AMERICA. 

77. TUBES A booklet for the beginner who is interested 
in vacuum tubes. A non-technical consideration of the 
various elements in the tube as well as their position in the 
receiver. CLEARTRON VACUUM TUBE COMPANY. 

87. TUBE TESTER A complete description of how to 
build and how to operate a tube tester. BURTON-ROGERS 
COMPANY. 

91. VACUUM TUBES A booklet giving the characteristics 
and uses of various types of tubes. This booklet may be 
obtained in English, "Spanish, or Portuguese. DEFOREST 
RADIO COMPANY. 

92. RESISTORS FOR A. C. OPERATED RECEIVERS A 
booklet giving circuit suggestions for building a. c. operated 
receivers, together with a diagram of the circuit used with 
the new ^oo-milliampere rectifier tube. CARTER RADIO 
COMPANY. 

97. HIGH-RESISTANCE VOLTMETERS A folder giving in- 
formation on how to use a high-resistance voltmeter, 
special consideration being given the voltage measurement 
of socket-power devices. WESTINGHOUSE ELECTRIC & 
MANUFACTURING COMPANY. 

102. RADIO POWER BULLETINS Circuit diagrams, theory 
constants, and trouble-shooting hints for units employing 
the BH or B rectifier tubes. RAYTHEON MANUFACTURING 
COMPANY. 

103. A. C. TUBES The design and operating character- 
istics of a new a. c. .tube. Five circuit diagrams show how 
to convert well-known circuits. SOVEREIGN ELECTRIC Jv 
MANUFACTURING COMPANY. 



MISCELLANEOUS 



38. 



LOG SHEET A list of broadcasting stations with 
columns for marking down dial settings. U. S. L. RADIO, 



adcasting station 
ettings. U. S. L. 
INCORPORATED. 

41. BABY RADIO -TRANSMITTER OF PXH-QEK Descrip- 
tion and circuit diagrams of dry-cell operated transmitter. 
BURGESS BATTERY COMPANY. 

42. ARCTIC RADIO EQUIPMENT Description and circuit 
details of short-wave receiver and transmitter used in 
Arctic exploration. BURGESS BATTERY COMPANY. 

43. SHORT-WAVE RECEIVER OF gxn-gEK Complete 
directions for assembly and operation of the receiver. 
BURGESS BATTERY COMPANY. 

58. How TO SELECT A RECEIVER A commonsense 
booklet describing what a radio set is, and what you should 
expect from it, in language that any one can understand. 
DAY-FAN ELECTRIC COMPANY. 

67. WEATHER FOR RADIO A very interesting booklet 
on the relationship between weather and radio reception, 
with maps and data on forecasting the probable results 
TAYLOR INSTRUMENT COMPANIES. 

73. RADIO SIMPLIFIED A non-technical booklet giving 
pertinent data on various radio subjects. Of especial in- 
terest to the beginner and set owner. CROSLEY RADIO COR- 
PORATION. 

74. THE EXPERIMENTER A monthly publication which 
gives technical facts, valuable tables, and pertinent informa- 
tion on various radio subjects. Interesting to the experi- 
menter and to the technical radio man. GENERAL RADIO 
COMPANY. 

75. FOR THE LISTENER General suggestions for the 
selecting, and the care of radio receivers. VALLEY ELECTRIC 
COMPANY. 

76. RADIO INSTRUMENTS A description of various 
meters used in radio and electrical circuits together with a 
short discussion of their uses. JEWELL ELECTRICAL IN- 
STRUMENT COMPANY. 

78. ELECTRICAL TROUBLES A pamphlet describing 
the use of electrical testing instruments in automotive work 
combined with a description of the cadmium test for stor- 
age batteries. Of interest to the owner of storage batteries. 
BURTON ROGERS COMPANY. 

95. RESISTANCE DATA Successive bulletins regarding 
the use of resistors in various parts of the radio circuit. 
INTERNATIONAL RESISTANCE COMPANY. 

06. VACUUM TUBE TESTING A booklet giving pertinent 
data on how to test vacuum tubes with special reference to 
a tube testing unit. JEWELL ELECTRICAL INSTRUMENT 
COMPANY. 

98. COPPER SHIELDING A booklet giving information 
on the use of shielding in radio receivers, with notes and 
diagrams showing how it may be applied practically. Of 
special interest to the home constructor. THE COPPER AND 
BRASS RESEARCH ASSOCIATION 

09. RADIO CONVENIENCE OUTLETS A folder giving 
diagrams and specifications for installing loud speakers in 
various locations at some distance from the receiving set. 
YAXLEY MANUFACTURING COMPANY. 



USE THIS BOOKLET COUPON 
1 RADIO BROADCAST SERVICE DEPARTMENT 

RADIO BROADCAST, Garden City, N. Y. 
Please send me (at no expense) the following book- 
1 lets indicated by numbers in the published list above: 



Name. 
Address. 



(Name) 



(Street} 



(City} (State) 

ORDER BY NUMBER ONI Y 
1 This coupon must accompany every request. RB 1 1-27 



The final improvement 
to be made in your set, 
install 




MODERN 

Type M Transformers 

Regardless of how perfectly your set may 
be working, there is still finer reception in 
store for you. The performance of Modern 
Type M Transformers represents such an 
advance in audio amplification that they 
represent a new standard by which trans- 
formers may be judged. They combine 
high inductance, large core and wire sizes 
and perfectly proportioned windings. Im- 
pedances have been carefully matched to 
the units with which they must work. 

The result is an almost flat performance 
curve with full response at 30 cycles and 
all harmonics and over amplified high 
notes fully eliminated. 

Satisfactory performance of Type M 
Transformers is guaranteed. Prices 1st 
and 2nd stage, $8.50 each; Output $8.00; 
Push-Pull, $10.00 each. 

Mail coupon below for blue- 
print folder showing Type M 
audio amplifying circuits 




MODERN 

"B" Compact 

A Raytheon "B" power unit that has been 
proven dependable and is guaranteed. 
Price $26.50 without tube. Sent by mail, 
postpaid, if your dealer cannot supply you. 

The Modern Electric Mfg. Co. 

Toledo, Ohio 



The Modern F.lectric Mfg. Co. 
Toledo, Ohio 

Please send prints of Typ. M audio circuits. I en- 
close 2c stamp. 

Name 

Address 

City 



R.B.-n 



RADIO BROADCAST ADVERTISER 






FILTER 



~s .. 



^ 



/X= 



/K4 7-/0A/A L. 



r a 



~*S ,67.. 



K3 

\!S 



AN ENTIRELY NEW AND UNIQUE 
HEAVY-DUTY BETTER-E 



Supplies 

Detector voltages, 11 to 45, adjustable; 
R. F. voltages from 50 to 75; 
A. F. voltages from 90 to 135; 
Power tube voltage 180 fixed. 

An Exclusive Feature 

Tubes and by-pass condensers are pro- 
tected against excessive and harmful 
voltages. 

Designed for lasting service with 
liberal factors of safety. 



A Strictly Heavy-Duty 
Power Unit 

Output rating is 70 mils at 180 volts. 
Uses R. C. A. UX-280 or Cunningham 
CX-380 Rectron. 

Licensed under patents of Radio 
Corporation of America and Associ- 
ated Companies. 

For 105-115 Volts, 50-60 cycles A. C. 
List price with cord, switch and plug, 
$40. Rectifier tube $5. 
Write National Co., Inc., W. A. Ready. 
Pres. Maiden, Mass, for new Bulletin B-124 



I ' a 

'Is I" i 





m <> i"i 

Type 7180 

A "B" That's Built for Service 

.9 our Exhibit, Booth No. *, Chicago SAow, Oc. 10th-l6th 



NATIONAL TUNING UNITS _ THE HEAVENLY TWINS 

More National Tuning Units have been used by set builders than all other similar components combined. 
o.-_j-.j .:_,. . ion Afpnnd By Tho OFFICIAL Desigio 

BROWNING & DRAKE 



Standard sincej 1923 



66 



RADIO BROADCAST ADVERTISER 



New AERO Circuit 

Worth Investigating 



The Improved Aero-Dyne 6 and the Aer 
and Aero 4 are destined to be immens 
popular this season! 



o 7 
sely 




AERO Universal Tuned Radio Frequency Kit 

Especially designed for the Improved Aero- 
Dyne 6. Kit consists of 4 twice-matched 
units. Adaptable to 201-A, 199, 112, and the 
new 240 and A. C. tubes. Tuning range be- 
low 200 to above 550 meters. 
This kit will make any circuit better in 
selectivity, tone and range. Will eliminate 
losses and give the greatest receiving effi- 
ciency. 

Code No. U- 16 (for .0005 Cond.) . ..$15.00 
Code No. U-163 (for .00035 Cond.)... 15.00 




AERO Seven Tuned Radio Frequency Kit 

Especially designed for the Aero 7. Kit con- 
sists of 3 twice-matched units. Coils are 
wound on Bakelite skeleton forms, assuring 
a 95% air di-electric. Tuning range from 
below 200 to above 550 meters. Adaptable 
to 201-A, 199, 112, and the new 240 and 
A. C. tubes. 

Code No. U- 12 (for .0005 Cond.) .. .$12.00 
Code No. U-123 (for .00035 Cond.)... 12.00 




AERO Four Kit 

An exceptionally efficient kit for use in the 
Aero 4 and other similar circuits. Consists 
of one Aero Universal Radio Frequency 
Transformer and one Aero Universal 3- 
Circuit Tuner. Uses 201-A, 112, 199 and new 
A. C. tubes. 

Code No. U.- 95 (for .0005 Cond.) $8.00 

Code No. U-953 (for .00035 Cond.) 8.00 

NOTE All AERO Universal Kit's for use in 
tuned radio frequency circuits have packed 
in each coil with a fixed prim iry a twice 
matched calibration slip showing reading 
of each fixed primary coil at 250 meters and 
at 500 meters; all having an accurate and 
similar calibration. 

A NEW SERVICE 

We have arranged to furnish the home set 
builder with complete Foundation Units for 
the above named Circuits and for the Chi- 
cago Daily News 4-Tube Receiver, drilled 
and engraved on Westinghouse Micarta. 
Detailed blueprints and wiring diagram for 
each circuit included in foundation units 
free. Write for information and prices. 

You should be able to get any of the above 

Aero Coils and parts from your dealer. If 

he should be out of stock order direct 

from the factory. 

AERO PRODUCTS, Inc. 

1772 Wilson Ave. Dept. 109 Chicago, 111. 



What Kit Shall I Buy? 

E list of kits herewith is printed as an exlen- 
sion of the scope of the Service Department of 
RADIO BROADCAST. // is our purpose to list here 
the technical data about kits on which information 
is available. In some cases, the kit can he pur- 
chased from your dealer complete; in others, the 
descriptive booklet is supplied for a small charge 
and the parts can be purchased as the buyer likes. 
The Service Department will not undertake to 
handle cash remittances for parts, but when the 
coupon on page 68 is filled out, all the informa- 
tion requested will be forwarded. 



20 1. SC FOUR-TUBE RECEIVER Single control. One 
stage of tuned radio frequency, regenerative detector, 
and two stages of transformer -coup led audio amplification. 
Regeneration control is accomplished by means of a variable 
resistor across the tickler coil. Standard parts; cost approxi- 
mately ^58.85. 

202. SC-11 FIVE-TUBE RECEIVERTWO stages of tuned 
radio frequency, detector, and two stages of trans- 
former-coupled audio. Two tuning controls. Volume control 
consists of potentiometer grid bias on r.f. tubes. Standard 
parts cost approximately $60.35. 

203. "HI-Q" KIT A five-tube tuned radio-frequency set 
having two radio stages, a detector, and two transformer- 
coupled audio stages. A special method of coupling in the 
i.f. stages tends to make the amplification more nearly equal 
over the entire band. Price $63. 05 without cabinet. 

204. R. G. S. KIT A four-tube inverse reflex circuit, 
having the equivalent of two tuned radio-frequency stages, 
detector, and three audio stages. Two controls. Price $69. 70 
without cabinet. 

205. PIERCE AIRO KIT A six-tube single-dial receiver; 
two stages of radio-frequency amplification, detector, and 
three stages of resistance -coup led audio. Volume control 
accomplished by variation of filament brilliancy of r.f. 
tubes or by adjusting compensating condensers. Complete 
chassis assembled but not wired costs $42.50. 

206. H & H-T. R. F. ASSEMBLY A tive-tube set; three 
tuning dials, two steps of radio frequency, detector, and 2 
transformer-coupled audio stages. Complete except for base- 
board, panel, screws, wires, and accessories. Price $30.00. 

207. PREMIER FIVE-TUBE ENSEMBLE Two stages of 
tuned radio frequency, detector, and two steps of trans- 
former-coupled audio. Three dials. Parts assembled but 
not wired. Price complete, except for cabinet, $35.00. 

208. "QUADRAFORMER VI" A six-tube set with two tun- 
ing controls. Two stages of tuned radio frequency using 
specially designed shielded coils, a detector, one stage of 
transformer-coupled audio, and two stages of resistance- 
coupled audio. Gain control by means of tapped primaries 
on the r.f. transformers. Essential kit consists of three 
shielded double-range "Quadraformer" coils, a selectivity 
control, and an "Ampitrol," price $17. 50. Complete parts 
$70.15. 

209. GEN-RAL FIVE-TUBE SET Two stages of tuned 
radio frequency, detector, and two transformer-coupled 
audio stages. Volume is controlled by a resistor in the plate 
circuit of the r.f. tubes. Uses a special r.f. coil ("Duo- 
Former") with figure eight winding. Parts mounted but 
not wired, price $37.50. 

210. BREMER-TULLY POWER-SIX A six-tube, dual- 
control set; three stages of neutralized tuned radio frequency, 
detector, and two transformer-coupled audio stages. Re- 
sistances in the grid circuit together with a phase shifting 
arrangement are used to prevent oscillation. Volume control 
accomplished by variation of B potential on r.f. tube. 
Essential kit consists of four r.f. transformers, two dual 
condensers, three small condensers, three choke coils, one 
5oo,ooo-ohm resistor, three i ^oo-ohm resistors, and a set 
of color charts and diagrams. Price $41.50. 

212. INFRADYNE AMPLIFIER A three-tube intermediate- 
frequency amplifier for the super-heterodyne and other 
special receivers, tuned to 3400 kc. (86 meters). Price $25.00. 

213. RADIO BROADCAST "LAB" RECEIVER A four-tube 
dual-control receiver with one stage of Rice neutralized 
tuned-radio frequency, regenerative detector (capacity 
controlled), and two stages of transformer-coupled audio. 
Approximate price, $78.15. 

214. LC-27 A five-tube set with two stages of tuned- 
radio frequency, a detector, and two stages of transformer- 
coupled audio. Special coils and special means of neutralizing 
are emp oyed. Output device. Price $85. 20 without cabinet. 

215. LOFTIN-WHITE A five-tube set with two stages of 
radio freouency, especially designed to give equal amplifica- 
tion at all frequencies, a detector, and two stages of trans- 
former-coupled audio. Two controls. Output device. Price 
$85.10. 

216. K.H.-27 A six-tube receiver with two stages of 
neutralized tuned radio frequency, a detector, three stages 
of choke-coupled audio, and an output device. Two controls. 
Price $86.00 w thout cabinet. 

217. AERO SHORT-WAVE KIT Three plug-in coils de- 
signed to operate with a regenerative detector circuit and 
having a frequen y range of from ig.QQOto 2306 kc. (15 to 130 
meters). Coils and plug only, price $12. 50. 

218. DiAMOND-OF-THE-AiR A five-tube set having one 
stage of tuned-radio frequency, a regenerative detector. 
one stage of transformer-coupled audio, and two stages of 
resistance-coupled audio. Volume control through regenera- 
tion, Two tuning dials. 

210. NORDEN-HAUCK SUPER 10 Ten tubes; five stages of 
tuned radio frequency, detector, and four stages of choke- 
and transformer-coupled audio frequency. Two controls. 
Price $291.40. 

220. BROWNING-DRAKE Five tubes; one stage tuned 
radio frequency (Rice neutralization), regenerative detector 
(tickler control), three stages of audio (special combination 
of resistance- and impedance-coupled audio). Two controls. 




Use an Aerial Kit 
lo qet Matched Parts 

Every part of your aerial 
installation should be of uni- 
formly high quality, because 
one poor unit wUl affect 
the entire job. 

For complete satisfaction 
year in and year out, buy 
a Belden Aerial Kit with 
Beldenamel Aerial Wire 
and the well-known Belden 
Lightning Arrester. Don't 
take a chance with a poor 
antenna system. Ask your 
dealer for a Belden Aerial kit. 

Belden Manufacturing Co. 

X51X-A S. Western Ave., Chicago 




BcMm 

Aerial Kit 



RADIO BROADCAST ADVERTISER 



67 






Your "B" Battery Eliminator 

will give you better service with 

R- 




(Trade Mark Registered) 




Gaseous 

Rectifier Tubes 



ARE BETTER 



6O Milliamperes - $4.5O 

85 Milliamperes - 4.5O 

4OO Milliamperes - 7.OO 

Ask for Catalog of full line of Standard Tubes. 

Guaranteed 

The standing of the Q-R-S Company, manu- 
facturers of quality merchandise for over a 
quarter of a century, establishes your saiety. 

Orders placed by the leading Eliminator Man- 
ufacturers for this season's delivery, approxi- 
mating Four Million Dollars' worth of Q-R-S 
Rectifier Tubes, establishes the approval of 
Radio Engineers. Ask any good dealer. 



THE Q :S COMPANY 

Manufacturers 
Executive Offices: 3O6 S. Wabash Ave., Chicago 

Factories: Chicago New York San Francisco Toronto, Canada Sydney, Australia Utrecht, Holland 
Established 1900. References Dun, Bradttreet, or any bank anywhere 




68 



RADIO BROADCAST ADVERTISER 



Radio Is BETTER With Dry Battery Power 




Lou can candle 
an e-but not 



a battery 



IHERE isn't much difference 
in the size or shape of batteries. 
And you can't tell how good 
they are before you use them. 
(( If you could, one element 
alone would win your prefer- 
ence for Burgess. That element 
is Chrome. ((Chrome is the pre- 
servative that maintains an 
abundance of unfailing energy 
in Burgess Batteries long after 
mostdry cells ceasetofunction. 
The black and white stripes 
are individual marks for iden- 
tifying Burgess Chrome Batter- 
ies. Buy them for long lasting, 
dependable performance! 

the preserving element 
sed in leather, metals, 
paints and other materials 
subject to wear, is also used in Burgess Bat- 
teries. It gives them unusual staying power. 
Burgess Chrome Batteries are patented. 



ny 'Rjidio Engineer 

BURGESS BATTERY COMPANY 

GmeralSales Office: CHICAGO 

Canadian Factories and Offices: 
Niagara Falls and Winnipeg 




URGESS 

FLASHLIGHT & RADIO 

BATTERIES 



WHAT KIT SHALL I BUY? (Continued) 

221. LR4 ULTRADYNE Nine-tube super-heterodyne; one 
stage of tuned radio frequency, one modulator, one oscillator, 
three intermediate-frequency stages, detector, and two 
transformer-coupled audio stages. 

222. GREIFF MULTIPLEX Four tubes (equivalent to six 
tubes); one stage of tuned radio frequency, one stage of 
transformer-coupled radio frequency, crystal detector, two 
stages of transformer-coupled audio, and one stage of 
impedance-coupled audio. Two controls. Price complete 
parts, $50.00. 

223. PHONOGRAPH AMPLIFIER A five-tube amplifier de- 
vice having an oscillator, a dectector, one stage of trans- 
former-coupled audio, and two stages of impedance-coupled 
audio. The phonograph signal is made to modulate the 
oscillator in much the same manner as an incoming signal 
from an antenna. 

224. BROWNING-DRAKE Five tubes; one stage tuned 
radio frequency (with special neutralization system), re- 
generative detector (tickler control), three stages of audio 
(special combination of resistance- and impedance-coup ed 
audio). Two controls. 

225. AERO Shoit-Wave Transmitting Kit consists of inter- 
changeable coils to be used in tuned-plate tuned grid circuit. 
Kits of coils, two choke coils, and mountings, can be secured 
for 20-40 meter band, 40-80 meter band, or 90-180 meter 
band for $12.00 



USE THIS COUPON FOR KITS 



| RADIO BROADCAST SERVICE DEPARTMENT 

1 Garden City, New York. 

| Please send me information about the following kits in- 

| dicated by number: 



Name. 
Address . 



(Number) 



(Street) 



(City) (State) 

ORDER BY NUMBER ONLY. This coupon must 

accompany each order. 

RB 11-27 



Thumb Nail Reviews 

WLS A skit having to do with various and 
droll adventures around the lion's cage in a circus 
and centering about one J. Walter Sapp. The 
mechanically simulated lions' roars were per- 
fectly swell. As for the spoken lines, they were 
not at all bad, but suffered from high-schoolish 
and unconvincing delivery a frequent enough 
radio play complaint. 

WOR The Kapellmeister String Quartet, ex- 
cellent interpreters of chamber music, playing on 
this occasion the Schubert Quartet in D minor. 
WBBM The station's own string trio perform- 
ing its routine tasks with great gusto and a 
splendid attack. 

WJZ The Arion Male Chorus singing "Sleep 
Kentucky Babe" in mellow fashion and introduc- 
ing some tricky guitar effects against a back- 
ground of humming. 

JOHN WALLACE. 



USE THIS COUPON FOR COMPLETE SETS 

RADIO BROADCAST SERVICE DEPARTMENT 

RADIO BROADCAST, Garden City, New York. 
Please send me information about the following manu- 
factured receivers ndicated bv number: 



Name 



Address . . 



(Number) 



(Street} 



(City) (State) 

ORDER BY NUMBER ONLY 
This coupon must accompany each order. RB 1 1-27 





The Newest ABC Power 
Supply Unit 

used with RCA 226 and 227 A C tubes 
and the Raytheon BH tube 



No. 5552 

$20.00 

List 



This latest development of the Dongan 
laboratories combines in one small, 
compact case the essential transfor- 
mers and chokes designed for use with 
R. C. A. 226 and 227 A. C. Filament 
Tubes (also UXi7i power amplifier 
tube) and the Raytheon BH Rectifier 
Tube. Complete power supply is se- 
cured, eliminating the need of batter- 
ies and charger. R. C. A. 226 and 
227 A. C. tubes also take the place of 
standard 201 A tubes. 
For complete information write to 
Dongan laboratories. If your dealer 
cannot supply you send check or 
money order direct. 

DONGAN ELECTRIC MFG. CO. 

2991-3001 Franklin St., Detroit, Michigan 




Eternal Life 

We cannot guarantee eternal life, but we 
do guarantee the AEROVOX FILTER 
CONDENSER when properly used to out- 
last all the(her equipment used in 
conjunction with it. 

WHY??? 

Because 

each section of a block is 
individually sealed and impregnated 
against moisture absorption. 

the safety factor used in 
manufacture, testing and rating will per- 
mit indefinite continuous operation at the 
rated working voltage without injury. 

For all eliminators 



"'Buill <Btlttr" 
70 Wuhington St.. Brooklyn, N. Y. 



RADIO BROADCAST ADVERTISER 




Ktrliunrf I-.*. 
Hut l.:7.Sil:,- of 





Typ. GSX.280 

FullWavef ' " 

Pric. $5.50 



es 
Best reception 

New broadcast /ievelop- 
ments make it necessary to 
have the latest types of tubes 
for fullest enjoyment of your 
receiving set. 

Bring it up to date with a 
complete installation of the 
new Gold Seal radio tubes 
specially developed for mod- 
ern reception. You will be 
delighted with the improve- 
ment. 

You can make the changes 
yourself no trouble. Our 
new booklet tells you all 
about it. Send today for your 
copy it is free. Use coupon 
below. 

All Standard Types 



~! 

., Inc. I 



| Gold Seal Electrical Co 

I ISO Park Ave., New York 

Send me copy of the new booklet. 
I 
I Name 



I Address I 

K.B.11.37 I 



Gold Seat 

Radio Tubes 



When Static Ruins Good 
Programs -Switch^ 
Over to 




Dubilier 

LIGHT-SOCKET AERIAL 



Just connect this neat little device to 
your set, plug into the nearest light- 
socket and listen to the difference! 
It takes only one program to convince 
you that crazy poles, loose wires, lead- 
ins, etc., are not only unnecessary, but 
downright inefficient when compared 
to the Dubilier Light Socket Aerial. 
Works perfectly on AC or DC, totally 
eliminates the lightning hazard and uses absolutely no current. 

Sold at all good radio stores on a 5-day money-back basis. Price $ 1 .50. 

Used in the Power-Units 
You Consider Best 

Dubilier Condenser Blocks are the choice of 
manufacturers whose battery eliminators are 
known for reliability and long life. In building 
your own unit remember that the condenser 
blocksarethemostexpensiveand important ele- 
ments in the circuit. Make sure that yours will 
stand heavy loads and long hours of service by 
insisting on Dubilier. Diagrams upon request. 




Dubilier Micadon 

The Standard Fixed Condenser of Radio in 
a new case of moulded Bakelite. shaped to 
meet the newest type of receiver construc- 
tion. Terminals adapted to either screwed 
or soldered connections. All standard ca- 
pacities. Priced from 45c to $ 1 .50. 



Dubilier Metaleak 

Accurate resistance ratings and extremely 
quiet performance make these tubular grid 
leak* popular with amateurs who build with 
great care. They are small, but highly im- 
portant items in the construction of any type 
of receiver. All .tandard resistance prices 
75c and 50c. 



DUBILIER CONDENSER CORP., 4377 Bronx Blvd., New York 

Dubilier 



CONDENSERS 



70 



RADIO BROADCAST ADVERTISER 



"RADIO BROADCASTS" DIRECTORY OF 
MANUFACTURED RECEIVERS 



I A coupon will be found on page 68. All readers who desire additional 
information on the receivers listed below need only insert the proper num- 



bers in the coupon, mail it to the Service Department of RADIO BROADCAST, 
and full details will be sent. New sets are listed in this space each month. 



KEY TO TUBE ABBREVIATIONS 

99 60-mA. filament (dry cell) 

01-A Storage battery 0.25 amps, filament 

12 Power tube (Storage battery) 

71 Power tube (Storage battery) 

16-B Half-wave rectifier tube 

80 Full-wave, high current rectifier 

81 Half-wave, high current rectifier 

Hmu High-Mu tube for resistance-coupled audio 

20 Power tube (dry cell) 

10 Power Tube (Storage battery) 

00-A Special detector 

13 Full-wave rectifier tube 

26 Low-voltage high-current a. c. tube 

27 Heater type a. c. tube 



DIRECT CURRENT RECEIVERS 
NO. 424. COLONIAL 26 

Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans- 
former audio (01-A and 71). Balanced t. r. f. One to 
three dials. Volume control: antenna switch and poten- 
tiometer across first audio. Watts required: 120. Con- 
sole size: 34 x 38 x 18 inches. Headphone connections. 
The filaments are connected in a scries parallel arrange- 
ment. Price $250 including power unit. 

NO. 425. SUPERPOWER 

Five tubes: All 01-A tubes. Multiplex circuit. Two 
dials. Volume control: resistance in r. f. plate. Watts 
required: 30. Antenna: loop or outside. Cabinet sizes: 
table, 27 x 10 x 9 inches: console, 28 x 50 x 21. Prices: 
table, $135 including power unit: console, $390 includ- 
ing power unit and loud speaker. 

A. C. OPERATED RECEIVERS 

NO. 508. ALL-AMERICAN 77, 88, AND 99 
Six tubes; 3 t. r. f. (26), detector (27), 2 transformer 
audio (26 and 71). Rice neutralized t. r. f. Single drum 
tuning. Volume control: potentiometer in r. f. plate. 
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy, 
25 x 38 x 18 inches; No. 99 console, 27i x 43 x 20 inches. 
Shielded. Output device. The filaments are supplied 
by means of three small transformers. The plate supply 
employs a gas-filled rectifier tube. Voltmeter in a. c. 
supply line. Prices: No. 77, $150, including power unit; 
No. 88, $210 including power unit; No. 99, $285 in- 
cluding power unit and loud speaker. 

NO. 509. ALL-AMERICAN "DUET"; "SEXTET" 

Six tubes; 2 t. r. f. (99), detector (99), 3 transformer 
audio (99 and 12). Rice neutralized t.r.f. Two dials. 
Volume control: resistance in r.f. plate. Cabinet sizes: 
"Duet," 23x56x165 inches; "Sextet," 22} x 13} x 15} 
inches. Shielded. Output device. The 99 filaments are 
connected in series and supplied with rectified a.c., 
while 12 is supplied with raw a.c. The plate and fila- 
ment supply uses gaseous rectifier tubes. Milliammeter 
on power unit. Prices: "Duet," $160 including power 
unit; "Sextet," $220 including power unit and loud 
speaker. 

NO. 511. ALL-AMERICAN 80, 90, AND 115 

Five tubes; 2 t.r.f. (99), detector (99), 2 transformer 
audio (99 and 12). Rice neutralized t.r.f. Two dials. 
Volume control: resistance in r.f. plate. Cabinet sizes: 
No. 80, 23i x 12} x 15 inches; No. 90, 37} x 12 x 12} 
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi- 
vidually shielded. Output device. See No. 509 for 
power supply. Prices: No. 80, $135 including power 
unit; No. 90, $145 including power unit and compart- 
ment; No. 115, $170 including power unit, compart- 
ment, and loud speaker. 

NO. 510. ALL-AMERICAN 7 

Seven tubes; 3 t.r.f. (26), 1 untuned r.f. (26), detector 
(27), 2 transformer audio (26 and 71). Rice neutralized 
t.r.f. One drum. Volume control: resistance in r.f. 
plate. Cabinet sizes: "Sovereign" console, 30} x 60J 
x 19 inches; "Lorraine" Hiboy, 25} x 53 5 x 17} inches; 
"Forte" cabinet, 25} x 13} x 17} inches. For filament 
and plate supply: See No. 508. Prices: "Sovereign" 
$460; "Lorraine" $360; "Forte" $270. All prices include 
power unit. First two include loud speaker. 

NO. 401. AMRAD AC9 

Six tubes; 3 t.r.f. (99), detector (99), 2 transformer 
(99 and 12). Neutrodyne. Two dials. Volume control: 
resistance across 1st audio. Watts consumed: 50. Cabi- 
net size: 27 x 9 x 11| inches. The 99 filaments are con- 
nected in series and supplied with rectified a.c., while 
the 12 is run on raw a.c. The power unit, requiring two 
16-B rectifiers, is separate and supplies A, B, and C 
current. Price $142 including power unit. 

NO. 402. AMRAD ACS 

Five tubes. Same as No. 401 except one less r.f. 
stage. Price $125 including power unit. 

NO. 536. SOUTH BEND 

Six tubes. One control. Sub-panel shielding. Binding 
Posts. Antenna: outdoor. Prices: table, $130, Baby 
Grand console, $195. 

NO. 537. WALBERT 26 

Six tubes; five Kellogg a.c. tubes and one 71. Two 
controls. Volume control: variable plate resistance. 
Isofarad circuit. Output device. Battery cable. Semi- 
slm-kh-d. Antenna: 50 to 75 feet. Cabinet size: 10} x 
29j x 16; inches. Prices: $215; with lubes, $250. 



NO. 484. BOSWORTH, B5 

Five tubes; 2 t.r.f. (26), detector (99), 2 transformer 
audio (special a.c. tubes). T.r.f. circuit. Two dials. 
Volume control: potentiometer. Cabinet size: 23 x 7 
x 8 inches. Output device included. Price $175. 

NO. 406. CLEARTONE 110 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All tubes a. c. heater type. One or two dials. Volume 
control: resistance in r. f. plate. Watts consumed: 40. 
Cabinet size: varies. The plate supply is built in the 
receiver and requires one rectifier tube. Filament sup- 
ply through step down transformers. Prices range from 
$1 75 to $375 which includes 5 a.c. tubes and one rectifier 
tube. 

NO. 407. COLONIAL 25 

Six tubes; 2 t. r. f. (01-A), detector (99), 2 resistance 
audio (99). 1 transformer audio (10). Balanced t.r.f. 
circuit. One or three dials. Volume control: Antenna 
switch and potentiometer on 1st audio. Watts con- 
sumed: 100. Console size: 34 x 38 x 18 inches. Output 
device. All tube filaments are operated on a. c. except 
the detector which is supplied with rectified a.c. from 
the plate supply. The rectifier employs two 16-B tubes. 
Price $250 including built-in plate and filament supply. 

NO. 507. CROSLEY 602 BANDBOX 

Six tubes; 3 t.r.f. (26), detector (27), 2 transformer 
audio (26 and 71). Neutrodyne circuit. One dial. 
Cabinet size: 17} x 5J x 78 inches. The heaters for the 
a.c. tubes and the 71 filament are supplied by windings in 
B unit transformers available to operate either on 25 or 
60 cycles. The plate current is supplied by means of 
rectifier tube. Price $65 for set alone, power unit $60. 

NO. 408. DAY-FAN "DE LUXE" 

Six tubes; 3 t.r.f., detector, 2 transformer audio. AU 
01-A tubes. One dial. Volume control: potentiometer 
across r.f. tubes. Watts consumed: 300. Console size: 
30 x 40 x 20 inches. The filaments are connected in 
series and supplied with d.c. from a motor-generator 
set which also supplies B and C current. Output de- 
vice. Price $350 including pow'er unit. 

NO. 409. DAYCRAFT 5 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All a. c. heater tubes. Rellexed t.r.f. One dial. Volume 
control: potentiometers in r.f. plate and 1st audio. 
Watts consumed: 135. Console size: 34 x 36 x 14 inches. 
Output device. The heaters are supplied by means of 
a small transformer. A built-in rectifier supplies B 
and C voltages. Price $170, less tubes. The following 
have one more r.f. stage and are not reflexed: Day- 
craft 6, $195; Dayrole 6, $235; Dayfan 6, $110. All 
prices less tubes. 

NO. 469. FREED-E1SEMANN NR11 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. One dial. 
Volume control: potentiometer. Watts consumed: 150. 
Cabinet size: 19J x 10 x 10} inches. Shielded. Output 
device. A special power, unit is included employing a 
rectifier tube. Price $225 including NR-411 power unit. 

NO. 487. FRESHMAN 7F-AC 

Six tubes; 3 t.r.f. (26), detector (27), 2 transformer 
audio (26 and 71). Equaphase circuit. One dial. Volume 
control: potentiometer across 1st audio. Console size: 
24}x41}xl5 inches. Output device. The filaments and 
heaters and B supply are all supplied by one power unit. 
The plate supply requires one 80 rectifier tube. Price 
$175 to $350, complete. 

NO. 421. SOVEREIGN 238 

Seven tubes of the a.c. heater type. Balanced t.r.f. 
Two dials. Volume control: resistance across 2nd audio. 
Watts consumed: 45. Console size: 37 x 52 x 15 inches. 
The heaters are supplied by a small a. c. transformer, 
while the plate is supplied by means of rectified a.c 
using a gaseous type rectifier. Price $325, including 
power unit and tubes. 

NO. 517. KELLOGG 510, 511, AND 512 

Seven tubes; 4 t.r.f., detector, 2 transformer audio. 
All Kellogg a.c. tubes. One control and special zone 
switch. Balanced. Volume control: special. Output de- 
vice. Shielded. Cable connection between power supply 
unit and receiver. Antenna: 25 to 100 feet. Panel 7i2 
x 27} inches. Prices: Model 510 and 512, consoles, $495 
complete. Model 511, consolette, $365 without loud 
speaker. 

NO. 496. SLEEPER ELECTRIC 

Five tubes; four 99 tubes and one 71. Two controls. 
Volume control: rheostat on r.f. Neutralized. Cable. 
Output device. Power supply uses two 16-B tubes. 
Antenna: 100 feet. Prices: Type 64, table, $160: Type 
65, table, with built-in loud speaker, $175; Type 66, 
table, $175; Type 67, console, $235; Type 78, console, 
$265. 

NO. 538. NEUTROWOUND, MASTER ALLECTRIC 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and two 71 in push-pull amplifier). The 01-A 
tubes are in series, and are supplied from a 400-mA. 
rectifier. Two drum controls. Volume control: variable 
plate resistance. Output device. Shielded. Antenna: 
50 to 100 feet. Price: $360 



NO. 413. MARTI 

Six tubes: 2 t.r.f., detector, 3 resistance audio. All 
tubes a.c. heater type. Two dials. Volume control: 
resistance in r.f. plate. Watts consumed: 38. Panel size 
7 x 21 inches. The built-in plate supply employs one 
16-B rectifier. The filaments are supplied by a small 
transformer. Prices: table, $235 including tubes and 
rectifier; console, $275 including tubes and rectifier; 
console, $325 including tubes, rectifier, and loud speaker. 

NO. 417 RADIOLA 28 

Eight tubes; five type 99 and one type 20. Drum 
control. Super-heterodyne circuit. C-battery connec- 
tions. Battery cable. Headphone connection. Antenna: 
loop. Set may be operated from batteries or from the 
power mains when used in conjunction with the model 
104 loud speaker. Prices: $260 with tubes, battery 
operation; $570 with model 104 loud speaker, a. c. 
operation. 

NO. 540 RADIOLA 30-A 

Receiver characteristics same as No. 417 except that 
type 71 power tube is used. This model is designed to 
operate on either a. c. or d. c. from the power mains. 
The combination rectifier power amplifier unit uses 
two type 81 tubes. Model 100-A loud speaker is con- 
tained in lower part of cabinet. Either a short indoor 
or long outside antenna may be used. Cabinet size: 
42'/2 x 29 x 17% inches. Price: $495. 

NO. 541 RADIOLA 32 

This model combines receiver No. 417 with the model 
104 loud speaker. The power unit uses two type 81 
tubes and a type 10 power amplifier. Loop is completely 



NO. 539 RADIOLA 17 

Six tubes; 3 t. r. f. (26), detector t27). 2 transformer 
audio (26 and 27). One control. Illuminated dial. 
Built-in power supply using type 80 rectifier. Antenna: 
100 feet. Cabinet size: 25! r ;, x 7'/ 8 x 8'/i. Price: $130 
without accessories. 

NO. 545. NEUTROWOUND, SUPER ALLECTRIC 

Five tubes; 2 t.r.f. (99), detector (99), 2 audio (99 
and 71). The 99 tubes are in series and are supplied from 
an 85-mA. rectifier. Two drum controls. Volume con- 
trol: variable plate resistance. Output device. Antenna: 
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price: 
$150. 

NO. 490. MOHAWK 

Six tubes; 2 t.r.f., detector, 2 transformer audio. All 
tubes a.c heater type except 71 in last stage. One di?l 
Volume control: rheostat on r.f. Watts consumed: 40 
Panel size: 12} x 8J inches. Output device. The heaters 
for the a.c tubes and the 71 filament are supplied by 
small transformers. The plate supply is of the built-in 
type using a rectifier tube. Prices range from $65 to 
S245 

NO. 522. CASE, 62 B AND 62 C 

McCullough a.c. tubes. Drum control. Volume con- 
trol; variable high resistance in audio system. C-battery 
connections. Semi-shielded. Cable. Antenna: 100 feet 
Panel size: 7 x 21 inches. Prices: Model 62 B, complete 
\vith a.c. equipment, $185; Model 62 C, complete with 
a.c. equipment, $235. 

NO. 523. CASE, 92 A AND 92 C 

McCullough a.c. tubes. Drum control. Inductive 
volume control. Technidyne circuit. Shielded. Cable. 
C-battery connections. Model 92 C contains output 
device. Loop operated. Prices: Model 92 A, table, $350; 
Model 92 C, console, $475. 



BATTERY OPERATED RECEIVERS 
NO. 542. PFANSTIEHL JUNIOR SIX 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio. 
Pfanstiehl circuit. Volume control : variable resistance in 
r.f. plate circuit. One dial. Shielded. Battery cable. C- 
battery connections. Etched bronze panel. Antenna: out- 
door. Cabinet size: 9 x 20 x 8 inches. Price: $80, without 
accessories. 

NO. 512. ALL-AMERICAN 44, 45, AND 66 

Six tubes; 3 t.r.f. (01-A. detector) 01 -A, 2 transformer 
audio (01-A and 71). Rice neutralized t.r.f. Drum 
control. Volume control: rheostat in r.f. Cabinet sizes: 
No. 44. 21 x 10 x 8 inches; No. 55. 25 x 38 x 18 inches; 
No. 66, 27} x 43 x 20 inches. C-battery connections. 
Battery cable. Antenna: 75 to 125 feet. Prices: No. 44, 
$70: No. 55, $125 including loud speaker; No. 66, $200 
including loud speaker. 

NO. 428. AMERICAN C6 

Five tubes; 2 t.r.f. detector, 2 transformer audio. 
All 01-A tubes. Semi balanced t.r.f. Three dials. Plate 
current 15 mA. Volume control: potentiometer. Cabinet 
sizes: table, 20 x 8} x 10 inches; console, 36 x 10 x 17 
inches. Partially shielded. Battery cable. C-battery 
connections. Antenna: 125 feet. Prices: table, $30; 
console, $65 including loud speaker. 



RADIO BROADCAST ADVERTISER 



71 





8 Tube 



ensations/ 

1 Control 



Att 



8 Tube 

1 Control 



RETAIL 



Big Discount to Agent* 
From this Price 






Has Complete 
A-B Power Unit 

A REAL ALL ELECTRIC Radio with one of 
the best A-B power units on the market no 
batteries needed at the worWs lowest price. 
This Marwood can't be excelled at ANY price. 
If you have electricity in your home, just 
plug into the light socket and forget bat- 
teries. No more battery trouble and expense. 
Costs less than 2c a day to operate. Always 
have 100% volume. ALL ELECTRIC Radios 
are high priced because they are new. We 
cut profit to the bone and offer a $250.00 
outfit for $98.00 retail price. Big discount to 
Agents. Don't buy any Radio 'til you get 
details of this sensational new ALL ELKC- 
TRIC Marwood. 



All Electric 

or Battery Operation 

AGAIN Marwood is a year ahead with the 
Radio sensation of 1928 at a low price that 
smashes Radio profiteering. Here's the sensa- 
tion they're all talking about the marvt lous 8 
Tube Single Control Marwood for BATTERY or 
ALL ELECTRIC operation. Direct from the 
factory for only $69.00 retail price a price far 
below that of smaller, less powerful Radios. Big 
discount to Agents from this price. You can't 
beat this wonderful new Marwood and you can't 
touch this low price. Why pay more for less 
quality? To prove that Marwood can't be beat 
we let you use it on 30 Days' Free Trial in your 
own home. Test it in every way. Compare it 
with any -Radio for tone, quality, volume, dis- 
tance, selectivity, beauty. If you don't say that 
it is a wonder, return it to us. We take the risk. 

New Exclusive Features 

Do you want coast to coast with volume enough 
to fill a theatre? Do you want amazing distance 
that only super-power Radios like the Marwood 
It can get? Do you want ultra-selectivity to cut 
out interference? Then you must test this Mar- 
wood on 30 Days' Free Trial. An amazing 
surprise awaits you. A flip of your finger 
makes it ultra-selective or broad just as 
you want it. Every Marwood is perfectly 
BALANCED a real laboratory job. Its 
simple one drum control ge ts ALL the sta- 
tions on the wave hand with case. A beau- 
tiful, guaranteed, super-efficient Radio in 
handsome walnut cabinets and consoles. 
A radio really worth double our low price. 

Buy From Factory Save Half 

Why pay profits to several middlemen? A 
Marwood in any retail store would cost 
practically three times our low direct- 
from-the-factory price. Our policy is high- 
est quality plus small profit and enormous 
sales. You get the benefit. Marwood is a 
pioneer, responsible Radio, with a good 
reputation to guard. We insist on the best 
and we charge the least. If you want next 
year's improvements NOW you must get 
a Marwood the Radio that's a year ahead. 

AGENTS 

Make Big Spare Time Money 

Get yoxir own Radio at wholesale price. It's 
easy to get orders for the Marwood from 
your friends and neighbors Folks buy 
quick when they compare Marwood quality 
and low prices. \Ve want local agents and 
dealers In each territory to handle the enor- 
mous business created by our national 
advertising. Make *1OO a week or more in 
spare time demonstrating at home. No ex- 
perience or capital needed. We show you 
how. This Is the biggest season in Radio 
history. Everybody wants a Radio. Oet In 
now. Hush coupon for 30 .lays' Free Trial, 
beautiful catalog. Agents' Confidential 
Prices and Agents' New I'lan. 

MARWOOD RADIO CORP. 

5315 Ravenswood Avenue 
Department A-l 7 Chicago, Illinois 



^ 

RETAIL 
PRICE 

Big Di'count , 

i to A$enf 



. 
Price 



Get Our Discounts 

Before You Buy a Radio 

Don't buy any Radio 'till you get our big discounts and 
catalog. Save half and get a Radio that IS a Radio. Try 
any Marwood on 30 Days' Free Trial at our risk. Tune 
in coast to coast on loud speaker with enormous vol- 
ume, clear as a bell. Let your wife and children oper- 
ate it. Compare it with any Radio regardless of price. 
If you don't get the surprise of your life, return it. We 
take the risk. Don't let Marwood low prices lead you 
to believe Marwood is not the highest quality. We 
have smashed Radio prices. You save half. 

6 Tube 1 Control 

This is the Marwood 6 Tube, 1 Control for BATTERY or 
ALL ELECTRIC operation. Gets coast tocoant on loud 
speaker with great volume. Only $47.00 retail. Big dis- 
counts to Agents. Comes in handsome walnut cabinets 
and consoles. This low price cannot be equalled by 
any other high grade 6 tube Radio. Has the volume of 
any 7 tube set. If you want a 6 tube Radio you can't 
beat a Marwood and you can't touch our low price. 



$47 



RETAIL 
PRICE 

BigDiscoitnt 
to Agents 
frttni This 
Price 




MARWOOD RADIO CORPORATION 

5315 Ravenswood Ave., I)'it A-17, Chicago, 111. 
Send Agents' Confidential Prices, 3O Days' Free 
Trial. New Catiilofr and Agents' New Money 
Making Plan. No obligation on my part. 



Address 

St. or R.F.D 

City State.. 



RADIO BROADCAST ADVERTISER 



NO. 485. BOSWORTH B6 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Two dials. Volume control: 
variable grid resistances. Battery cable. C battery 
connections. Antenna: 25 feet or longer. Cabinet size 
15 x 7 x 8 inches. Price $75. 

NO. 513. COUNTERPHASE SIX 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 12). Counterphase t.r.f. Two 
dials. Plate current: 32 mA. Volume control: rheosta. 
on 2nd and 3rd r.f. Coils shielded. Battery cable. C- 
battery connections. Antenna: 75 to 100 feet. Console 
size: 18J x 405 x 15} inches. Prices: Model 35, table, 
$110; Model 37, console, $175. 

NO. 514. COUNTERPHASE EIGHT 

Eight tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 12). 'Counterphase t.r.f. One 
dial. Plate current: 40 mA. Volume control: rheostat in 
1st r.f. Copper stage shielding. Battery cable. C-battery 
connections. Antenna: 75 to 100 feet. Cabinet size: 
30 x 12J x 16 inches. Prices: Model 12, table, $225' 
Model 16, console, $335; Model 18, console, $365. 

NO. 506. CROSLEY 601 BANDBOX 

Six tubes; 3 t.r.f., detector, 2 transformer audio. AH 
01-A tubes. Neutrodyne. One dial. Plate current: 
40 mA. Volume control: rheostat in r.f. Shielded. 
Battery cable. C-battery connections. Antenna: 75 to 
150 feet. Cabinet size: 175 x 5} x 7j. Price, $55. 

NO. 434. DAY-FAN 6 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 12 or 71). One dial. Plate 
current: 12 to 15 mA. Volume control: rheostat on r.f. 
Shielded. Battery cable, C-battery connections. Output 
device. Antenna: 50 to 120 feet. Cabinet sizes: Daycraft 
6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7 
Prices: Day-Fan 6, $110; Daycraft 6, $145 including 
loud speaker; Day-Fan Jr. not available. 

NO. 435. DAY-FAN 7 

Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 resist- 
ance audio (01-A), 2 transformer audio (01-A and 12 
or 71). Plate current: 15 mA. Antenna: outside. Same 
as No. 434. Price $115. 

NO. 503. FADA SPECIAL 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. Two drum 
control. Plate current: 20 to 24mA. Volume control: 
rheostat on r.f. Coils shielded. Battery cable. C-battery 
connections. Headphone connection. Antenna: outdoor. 
Cabinet size: 20$ x 13J x 10} inches. Price $95. 

NO. 504. FADA 7 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. Two drum 
control. Plate current: 43mA. Volume control: rheostat 
on r.f. Completely shielded. Battery cable. C-battery 
connections. Headphone connections. Output device. 
Antenna: outdoor or loop. Cabinet sizes: table, 25J x 
131 x Hi inches; console, 29 x 50 x 17 inches. Prices: 
table, $185; console, $285. 

NO. 436. FEDERAL 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 12 or 71). Balanced t.r.f. One 
dial. Plate current: 20.7 mA. Volume control: rheostat 
on r.f. Shielded. Battery cable. C-battery connections. 
Antenna: loop. Made in 6 models. Price varies from 
$250 to $1000 including loop. 

NO. 505. FADA 8 

Eight tubes. Same as No. 504 except for one extra 
stage of audio and different cabinet. Prices: table, $300; 
console, $400. 

NO. 437. FERGUSON 10A 

Seven tubes; 3 t.r.f. (01-A), detector (01-A), 3 audio 
(01-A and 12 or 71). One dial. Plate current: 18 to 25 
mA. Volume control: rheostat on two r.f. Shielded. 
Battery cable. C-battery connections. Antenna: 100 
feet. Cabinet size: 214 x 12 x 15 inches. Price $150. 

NO. 438. FERGUSON 14 

Ten tubes; 3 untuned r.f., 3 t. r.f. (01-A), detector 
(01-A), 3 audio (01-A and 12 or 71). Special balanced 
t.r.f. One dial. Plate current: 30 to 35 mA. Volume con- 
trol: rheostat in three r.f. Shielded. Battery cable, C- 
battery connections. Antenna: loop. Cabinet size: 
24 x 12 x 16 inches. Price $235, including loop. 



NO. 439. FERGUSON 12 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 1 trans- 
former audio (01-A), 2 resistance audio (01-A and 12 
or 71). Two dials. Plate current: 18 to 25 mA. Volume 
control: rheostat on two r.f. Partially shielded. Battery 
cable. C-battery connections. Antenna: 100 feet. 
Cabinet size: 22* x 10 x 12 inches. Price $85. Consolette 
$145 including loud speaker. 

NO. 440. FREED-EISEMANN NR-8 NR-9, AND 
NR-66 

Six tubes; 3 t.r.f. (01-A), detector '01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. NR-8, two 
dials; others one dial. Plate current: 30 mA. Volume 
control: rheostat on r.f. NR-8 and 9: chassis type 
shielding. NR-66, individual stage shielding. Battery 
cable. C-battery connections. Antenna: 100 feet 
Cabinet sizes: NR-8 and 9, 19JxlOx 10}inches; NR-66 
20 x 10! x 12 inches. Prices: NR-8, $90; NR-9, $100; 
NR-66, $125. 

NO. 501. KING "CHEVALIER" 

Six tubes. Same as No. 500. Coils completely shielded. 
Panel si/e: 11x7 inches. Price, $210 including loud 
speaker. 



NO. 441. FREED-EISEMANN NR-77 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 
transformer audio (01-A and 71). Neutrodyne. One 
dial. Plate current: 35 mA. Volume control: rheostat on 
r.f. Shielding. Battery cable. C-battery connections. 
Antenna: outside or loop. Cabinet size: 23 x 10i x 13 
inches. Price $175. 

NO. 442. FREED-EISEMANN 800 AND 850 

Eight tubes; 4 t.r.f. (01-A), detector (01-A), 1 trans- 
former (01-A), 1 parallel audio (01-A or 71). Neutro- 
dyne. One dial. Plate current: 35 mA. Volume control: 
rheostat on r.f. Shielded. Battery cable. C-battery 
connections. Output: two tubes in parallel or one power 
tube may be used. Antenna: outside or loop Cabinet 
sizes: No. 800, 34 x 154 x 13J inches; No. 850, 36 x 65} x 
17}. Prices not available. 

NO. 444. GREBE MU 1 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 12 or 71). Balanced t.r.f. One, 
two, or three dials (operate singly or together). Plate 
current: 30mA. Volume control: rheostat on r.f. Bi- 
nocular coils. Binding posts. C-battery connections 
Antenna: 125 feet. Cabinet size: 22} x 9i x 13 inches 
Prices range from $95 to $320. 

NO. 426. HOMER 

Seven tubes; 4 t.r.f. (01-A); detector (01-A or OOA); 
2 audio (01-A and 12 or 71). One knob tuning control. 
Volume control : rotor control in antenna circuit. Plate 
current : 22 .0 25 mA. 'Technidyne" circuit. Completely 
enclosed in aluminum box. Battery cable. C-battery con- 
nections. Cabinet size, 8J x 19} x 9J inches. Chassis size, 
6{ x 17 x 8 inches. Prices: Chassis only, $80. Table cabi- 
net, $95. 

NO. 502. KENNEDY ROYAL 7. CONSOLETTE 

Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). One dial. Plate current: 
42 mA. Volume control: rheostat on two r.f. Special 
r.f. coils. Battery cable. C-battery connections. Head- 
phone connection. Antenna: outside or loop. Consolette 
size: 36} x 35} x 19 inches. Price $220. 

NO. 498. KING "CRUSADER" 

Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans- 
former audio (01-A and 71). Balanced t.r.f. One dial. 
Plate current: 20 mA. Volume control: rheostat on r.f. 
Coils shielded. Battery cable. C-battery connections. 
Antenna: outside. Panel: 11 x 7 inches. Price, $115. 

NO. 499. KING "COMMANDER" 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). Balanced t.r.f. One dial. 
Plate current: 25 mA. Volume control: rheostat on r f. 
Completely shielded. Battery cable. C-battery con- 
nections. Antenna: loop. Panel size: 12 x 8 inches. 
Price $220 including loop. 

NO. 429. KING COLE VII AND VIII 

Seven tubes; 3 t.r.f., detector, 1 resistance audio, 2 
transformer audio. All 01-A tubes. Model VIII has one 
more stage t.r.f. (eight tubes). Model VII, two dials. 
Model VIII, one dial. Plate current: 15 to 50 mA. 
Volume control: primary shunt in r.f. Steel shielding. 
Battery cable and binding posts. C-battery connections. 
Output devices on some consoles. Antenna: 10 to 100 
feet. Cabinet size: varies. Prices: Model VII, $80 to 
$160; Model VIII, $100 to $300. 

NO. 500. KING "BARONET" AND "VIKING" 

Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans- 
former audio (01-A and 71). Balanced t.r.f. One dial. 
Plate current: 19 mA. Volume control: rheostat in r.f. 
Battery cable. C-battery connections. Antenna: out- 
side. Panel size: 18 x 7 inches. Prices: "Baronet," $70; 
"Viking," $140 including loud speaker. 

NO. 489. MOHAWK 

Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio 
(01-A and 71). One dial. Plate current: 40 mA. Volume 
control: rheostat on r.f. Battery cable. C-battery con- 
nections. Output device. Antenna: 60 feet. Panel size: 
12} x &', inches. Prices range from $65 to $245. 

NO. 543. ATWATER KENT, MODEL 33 

Six tubes: 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71 or 1"). One dial. Volume control: r.f. fila- 
ment rheostat. C-battery connection*. Battery cable 
Antenna: 100 feet. Steel panel. Cabinet size: 21 Jx6|x6J 
inches. Price: $90, without accessories. 

NO. 544. ATWATER KENT, MODEL 50 

Seven tubes; 4 t.r. f. (01-A) , detector (01-A), 2 audio 
(01-A and 12 or 71 ). Volume control: r.f. filament rheo- 
stat. C-battery connections. Battery cable. Special band- 
pass filter circuit with an untuned amplifier. Cabinet 
size: 20f x 13 x 7J inches. Price: $150. 

NO. 452. ORIOLE 90 

F ve tubes; 2 t.r.f., detector, 2 transformer audio. 
All 01-A tubes. "Trinum" circuit. Two dials. Plate 
current: 18 mA. Volume control: rheostat on r. f. 
Battery cable. C-battery connections. Antenna: 50 to 
100 feet. Cabinet size: 25} x Hi x 12} inches. Price 
$85. Another model has 8 tubes, one dial, and is 
shielded. Price $185. 

NO. 453. PARAGON 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 3 double 
impedance audio (01-A and 71). One dial. Plate cur- 
rent: 40 mA. Volume control: resistance in r.f. plate. 
Shielded. Battery cable. C-battery connections. Out- 
put device. Antenna: 100 feet. Console size: 20 x 46 
x 1 7 inches. Price not determined. 



NO. 543 RADIOLA 20 



Five tubes; 2 t. r. f. (99), detector (99), two trans- 
former audio (99 and 20). Regenerative detector. Two 
drum controls. C-battery connections. Battery cable. 
Antenna: 100 feet. Price; $78 without accessories. 

NO. 480. PFANSTIEHL 30 AND 302 

Six tubes; 3 t.r.f. (01-A), detector (01- 2A), trans- 
former audio (01-A and 71). One dial. Plate current: 
23 to 32 mA. Volume control: resistance in r.f. plate. 
Shielded. Battery cable. C-battery connections. An- 
tenna: outside. Panel size. 17J x 8} inches. Prices: No 
30 cabinet, $105; No. 302 console, $185 including 
loud speaker. 

NO. 515. BROWNING-DRAKE 7-A 

Seven tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio 
(Hmu, two 01-A, and 71). Illuminated drum control. 
Volume control: rheostat on 1st r.f. Shielded. Neutral- 
ized. C-battery connections. Battery Cable. Metal 
panel. Output device. Antenna: 50-75 feet Cabinet 
30 x 1 1 x 9 inches. Price, $145. 

NO. 516. BROWNING-DRAKE 6-A 

Six tubes; 1 t.r.f. (99), detector (00-A), 3 audio 
(Hmu, two 01-A and 71). Drum control with auxiliary 
adjustment. Volume control: rheostat on r.f. Regenera- 
tive detector. Shielded. Neutralized. C-battery connec- 
tions. Battery cable. Antenna: 50-100 feet. Cabinet 
25 x 11 x9. Price $105. 

NO. 518. KELLOGG "WAVE MASTER," 
504, 505, AND 506. 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
One control and special zone switch. Volume control: 
rheostat on r.f. C-battery connections. Binding posts 
Plate current: 25 to 35 mA. Antenna: 100 feet. Panel 
7} x 25} inches. Prices: Model 504, table, $75, less 
accessories. Model 505, table, $125 with loud speaker 
Model 506, consolette, $135 with loud speaker. 

NO. 519. KELLOGG, 507 AND 508. 

Six tubes, 3 t.r.f., detector, 2 transformer audio. One 
control and special zone switch. Volume control: rheo- 
stat on r.f. C-battery connections. Balanced. Shielded. 
Binding posts and battery cable. Antenna: 70 feet. 
Cabinet size: Model 507, table, 30 x 13J x 14 inches 
Model 508, console, 34 x 18 x 54 inches. Prices: Model 
507, $190 less accessories. Model 508, $320 with loud 
speaker. 

NO. 427. MURDOCK 7 

Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 trans- 
former and 2 resistance audio (two 01-A and 12 or 71) 
One control. Volume control: rheostat on r.f. Coils 
shielded. Neutralized. Battery cable. C-battery con- 
nections. Complete metal case. Antenna: 100 feet. 
Panel size: 9 x 23 inches. Price, not available. 

NO. 520. BOSCH 57 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71). One control calibrated in kc. Volume 
control: rheostat on r.f. Shielded. Battery cable. C- 
battery connections. Balanced. Output device. Built-in 
loud speaker. Antenna: built-in loop or outside antenna. 
100 feet. Cabinet size: 46 x 16 x 30 inches. Price: $340 
including enclosed loop and loud speaker. 

NO. 521. BOSCH "CRUISER," 66 AND 76 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71). One control. Volume control: rheostat 
on r.f. Shielded. C-battery connections. Balanced 
Battery cable. Antenna: 20 to 100 feet. Prices: Model 
66, table, $99.50. Model 76, console, $175; with loud 
speaker $195. 

NO. 524. CASE, 61 A AND 61 C 

T.r.f. Semi-shielded. Battery cable. Drum control. 
Volume control: variable high resistance in audio sys- 
tem. Plate current: 35 mA. Antenna: 100 feet. Prices: 
Model 61 A, $85; Model 61 C, console, $135. 

NO. 525. CASE, 90 A AND 90 C 

Drum control. Inductive volume control. Technidyne 
circuit. C-battery connections. Battery cable. Loop 
operated. Model 90-C equipped with output device 
Prices: Model 90 A, table, $225; Model 90 C, console 
$350. 

NO. 526. ARBORPHONE 25 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71). One control. Volume control: rheostat. 
Shielded. Battery cable. Output device. C-battery con- 
nections. Loftin- White circuit. Antenna: 75 feet. Panel: 
7; x 15 inches, metal. Prices: Model 25, table, $125; 
Model 252, $185; Model 253, $250; Mode; 255, combin- 
ation phonograph and radio, $600. 

NO. 527. ARBORPHONE 27 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A). Two controls. Volume control: rheostat. C- 
battery connections. Binding posts. Antenna: 75 feet. 
Prices: Model 27, $65; Model 271, $99.50; Model 272, 
$125. 

NO. 528. THE "CHIEF" 

Seven tubes; six 01-A tubes and one power tube. 
One control. Volume control: rheostat. C-battery con- 
nection. Partial shielding. Binding posts. Antenna: 
outside. Cabinet size: 40 x 22 x 16 inches. Prices: 
Complete with A power supply, $250; without acces- 
sories, $150. 

NO. 529. DIAMOND SPECIAL, SUPER SPECIAL, 
AND BABY GRAND CONSOLE 

Six tubes; all 01 -A type. One control. Partial shield- 
ing. C-battery connections. Volume control: rheostat. 
Binding posts. Antenna: outdoor. Prices: Diamond 
Special, $75; Super Special, $65; Baby Grand Console, 
$110. 



RADIO BROADCAST ADVERTISER 



73 






Everything that Radio Has to Give 





Kingston service goes al! the way through, 
and Kingston dealers know that this 
company stands squarely behind its prod- 
ucts. The new Kingston B Ba.tery elimina- 
tor is fully guaranteed to be all and do all 
that is claimed for it. 



The Kingston B Supply Unit brings to your radio evenings a new 
richness and a new delight full tones, clearness and perfect reception 
always! It maintains your set at its perfection peak, operates silently, 
and forever removes the trouble and expense of batteries. The 
Kingston is beautifully made, is 
smartly finished in satin black, and 
is built by experts with extreme 
care and accuracy. There are pro- 
vided three voltage terminals, each 
adjustable over a wide range, mak- 
ing possible any desired voltages 
from 5 to 200. In keeping with 
Kingston quality, the Raytheon 
125 milliampere type BH tube is 
used as a rectifier. 




If your dealer can't supply you as^ us 

KOKOMO ELECTRIC CO. KOKOMO, IND. 



Type 2, for 11 0-1 20 Volt AC 50 or 60. 

Cycle Current, $35.00. 

For receiving sets having not more 
than eight lubes and not having type 
UXl?l power tube or equivalent, 

Type ZA, for 110-120 Volt AC 50 or 

60 Cycle Current, *-J2.50. 

For all S*MS using type UX171 power 
tube or equivalent and for all large 
sets having nine or more tubes. 

Type 2C, for 110-120 Volt AC 25, 30 
or 40 cycle current, #47.50. 

Price* include type BH Raytheon tube. 

Any of these models will be furnished 

with an automatic control switch built in 

the unit for $2*0 additional. With 

th ls the B unit is automatically 

vitched on or off when switch 

i the radio set panel 

is turned. 






LEAK 

CARBORUNDUM^ - 



SLIP a Carborundum Grid-Leak into your set and you will notice 
an improved reception instantly. 

Carborundum Grid-Leaks are quiet. They are dense solid rods of Car- 
borundum that provide for an uninterrupted flow of current. 

No chance for the creation of minute noisy arcs no glass tube. They 
can't disintegrate. They are unbreakable. 

All standard values, both Grid-Leaks and Fixed Resistors. 

The Grid-Leaks are tested for values at 5 volts the Resistors at 90 volts. 

No. 77 Carborundum Grid-Leaks, values 0.25, 0.50, 1 to 10 Megohms, each $0.50 

No. 79 Carborundum Resistors, values 2500 and 5000 Ohms, each 1.00 

No. 79 Carborundum Fixed Resistors, values 1 2,000, 25,000, 50,000, 75,000 and 100,000 Ohms, ea., .75 



From 

your dealer 
or direct 



THE CARBORUNDUM COMPANY, NIAGARA FALLS, N. Y. 

CANADIAN CARBORUNDUM CO., LTD., NIAGARA FALLS, ONT. 

Sales Offices and Warehouses in 

New York, Chicago. Boston, Philadelphia, Cleveland, Detroit, Cincinnati, Pittsburgh, Milwaukee, Grand Kapida 
Tbe Carborundum Co., Ltd., Manchester, Eng. Deutsche Carborundum Werke, Dusseldorf, Get. 

f Carborundum ii the Rejlitere.1 Trade Same ued by Tbe Carborundum Company for Sill- "[ 
I con Carbide. Tble Trade .Mark le tbe extln.i.e property of Tbe Carborundum Company. _1 




The 
Carborundum 

Company 
Niagara Falls, N.Y. 

nd booklet 1 >-_ 
jm in Radio" 



74 



RADIO BROADCAST ADVERTISER 



NO. 530. KOLSTER, 7A AND 7B 

Seven tubes: 4 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 12). One control. Volume control: rheostat 
on r.f. Shielded. Battery cable. C-battery connections. 
Antenna: 50 to 75 feet. Prices: Model 7A, $125; Model 
7B, with built-in loud speaker, $140. 

NO. 531. KOLSTER, 8A, 8B, AND 8C 

Eight tubes; 4 t.r.f. (01-A), detector (01-A), 3 audio 
(two 01-A and one 12). One control. Volume control: 
rheostat on r.f. Shielded. Battery cable. C-battery con- 
nections. Model 8A uses 50 to 75 foot antenna; model 
8B contains output device and uses antenna or detach- 
able loop; Model 8C contains output device and uses 
antenna or built-in loop. Prices: 8A, $185; 8B, $235; 
8C, $375. 

NO. 532. KOLSTER, 6D, 6G, AND 6H 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 12). One control. Volume control: rheostat 
on r.f. C-battery connections. Battery cable. Antenna: 
50 to 75 feet. Model 6G contains output device and 
built-in loud speaker; Model 6H contains built-in B 
power unit and loud speaker. Prices: Model 6D, $80; 
Model 6G, $165; Model 6H, $265. 

NO. 533. SIMPLEX, SR 9 AND SR 10 

Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 audio 
(01-A and 12). SR 9, three controls; SR 10, two con- 
trols. Volume control : rheostat. C-battery connections. 
Battery cable. Headphone connection. Prices: SR 9, 
table, $65; consolette, $95; console, $145. SR 10, table 
$70; consolette, $95; console, $145. 

NO. 534. SIMPLEX, SR 11 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 audio 
(01-A and 12). One control. Volume control: rheostat. 
C-battery connections. Battery cable. Antenna: 100 
feet. Prices: table, $70; consolette, $95; console, $145. 

NO. 535. STANDARDYNE, MODEL S 27 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio 
(power tubes). One control. Volume control: rheostat 
on r.f. C-battery connections. Binding posts. Antenna: 
75 feet. Cabinet size: 9 x 9 x 19} inches. Prices: S 27, 
$49.50; S 950, console, with built-in loud speaker, 
$99.50; S 600, console with built-in loud speaker, 
$104.50. 

NO. 481. PFANSTIEHL 32 AND 322 

Seven tubes: 3 t.r.f. (01-A), detector (01-A), 3 audio 
(01-A and 71). One dial. Plate current: 23 to 32 mA. 
Volume control: resistance in r. f.. plate. Shielded 
Battery cable. C-battery connections. Output device. 
Antenna: outside. Panel: 17J x 8} inches. Prices: No. 
32 cabinet, $145; No. 322 console, $245 including 
loud speaker. 



NO 433. ARBORPHONE 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All 01-A tubes. Two dials. Plate current: 16mA. Vol- 
ume control : rheostat in r.f. and resistance in r.f. plate. 
C-battery connections. Binding posts. Antenna: taps 
for various lengths. Cabinet size: 24 x 9 x 10$ inches. 
Price: $65. 

NO. 431. AUDIOLA 6 

Six tubes; 3 t.r.f. (01-A), detector (00-A). 2 trans- 
former audio (01-A and 71). Drum control. Plate cur- 
rent: 20 mA. Volume control: resistance in r.f. plate. 
Stage shielding. Battery cable. C-battery connection. 
Antenna: 50 to 100 feet. Cabinet size: 28} x 11 x 14} 
inches. Price not established. 

NO. 432. AUDIOLA 8 

Eight tubes; 4 t.r.f. (01-A), detector (00-A), 1 trans- 
former audio (01-A), push-pull audio (12 or 71). Bridge 
balanced t.r.f. Drum control. Volume control : resistance 
in r.f. plate. Stage shielding. Battery cable. C-battery 
connections. Antenna: 10 to 100 feet. Cabinet size: 
28} x 11 x 14} inches. Price not established. 

NO. 542 RADIOLA 16 

Six tubes; 3 t. r. f. (Ol-A), detector (Ol-A), 2 trans- 
former audio (01-A and 112). One control. C-battery 
connections. Battery cable. Antenna: outside. Cabinet 
size: 16'/ 2 x 8Vi x 7Vx inches. Price: $69.50 without ac- 
cessories. 

NO. 456. RADIOLA 20 

Five tubes: 2 t.r.f. (99), detector (99), 2 transformer 
audio (99 and 20). Balanced t.r.f. and regenerative de- 
tector. Two dials. Volume control: regenerative. 
Shielded. C-battery connections. Headphone connec- 
tions. Antenna: 75 to 1.50 feet. Cabinet size: 19} x 
111 x 16 inches. Price $115 including all tubes. 

NO. 457 RADIOLA 25 

Six tubes; five type 99 and one type 20. Drum con- 
trol. Super-heterodyne circuit. C-battery connections. 
Battery cable. Headphone connections. Antenna: loop. 
Set may be operated from batteries or from power mains 
when used with model 104 loud speaker. Price; $165 
with tubes, for battery operation. Apparatus for opera- 
tion of set from the power mains can be purchased 
separately. 

NO. 493. SONORA F 

Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). Special balanced t.r.f. 
Two dials. Plate current: 45 mA. Volume control: 
rheostat in r.f. Shielded. Battery cable. C-battery 
connections. Output device. Antenna: loop. Console 
si/: 32 x 45} x 17 inches. Prices range from $350 to 
$-450 including loop and loud speaker. 



NO. 494. SONORA E 

Six tubes; 3 t.r.f. (01-A), detector fOO-A), 2 trans- 
former audio (01-A and 71). Special balanced t.r.f. 
Two dials. Plate current: 35 to 40 mA. Volume control: 
rheostat on r.f. Shielded. Battery cable. C-battery 
connections. Antenna: outside. Cabinet size: varies. 
Prices: table, $110; semi-console, $140; console, $240 
including loud speaker. 

NO. 495. SONORA D 

Same as No. 49'. except arrangement of tubes; 2 
t.r.f., detector, 3 audio. Prices: table, $125; standard 
console, $185; "DeLuxe" console, $225. 

NO. 482. STEWART-WARNER 705 AND 710 

Six tubes; 3 t.r.f., detector, 2 transformer audio. 
All 01-A tubes. Balanced t.r.f. Two dials. Plate cur- 
rent: 10 to 25 mA. Volume control: resistance in r.f. 
plate. Shielded. Battery cable. C-battery connections. 
Antenna: 80 feet. Cabinet sizes: No. 705 table, 26} 
x 111 x 13}g inches; No. 710 console, 29j x 42 x 17} 
inches. Tentative prices: No. 705, $115; No. 710 
$265 including loud speaker. 

NO. 483. STEWART-WARNER 525 AND 520 

Same as No. 482 except no shielding. Cabinet sizes: 
No. 525 table, 19} x 10 x 11 J inches; No. 520 console, 
22} x 40 x 14 H inches. Tentative prices: No. 525, $75; 
No. 520, $117.50 including loud speaker. 

NO. 459. STROMBERG-CARLSON 501 AND 502 

Five tubes; 2 t.r.f. (01-A). detector (00-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. Two dials. 
Plate current: 25 to 35 mA. Volume control: rheostat 
on 1st r.f. Shielded. Battery cable. C-battery connec- 
tions. Headphone connections. Output device. Panel 
voltmeter. Antenna: 60 to 100 feet. Cabinet sizes: 
No. 501, 25} x 13 x 14 inches; No. 502, 28 )j x 50 
A * 16J inches. Prices: No. 501, $180; No. 502, $290. 

NO. 460. STROMBERG-CARLSON 601 AND 602 

Six tubes. Same as No. 549 except for extra t.r.f. 
stage. Cabinet sizes: No. 601, 27A x 16} x I4f, inches; 
No. 602, 28} x 51} x 19i 5 inches. Prices: No. 601, $225; 
No. 602, $330. 

NO. 486. VALLEY 71 

Seven tubes; 4 t.r.f. (01-A), detect9r (01-A), 2 trans- 
former audio (01-A and 71). One dial. Plate current: 
35 mA. Volume control: rheostat on r.f. Partially 
shielded. Battery cable. C-battery connections. Head- 
phone connection. Antenna: 50 to 100 feet. Cabinet 
size: 27 x 6 x 7 inches. Price $95. 

NO. 472. VOLOTONE VIII 

Six tubes. Same as No. 471 with following excep- 
tions; 2 t.r.f. stages. Three dir.ls. Plate current: 2- 
mA. Cabinet size: 26.J x 8 x 12 inches. Price $140. 



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BRUNO QUARTZITE TUNING COILS 
have been repeatedly specified in new cir- 
cuits for their high degree of efficiency, selec- 
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The No. 99 Jr. Tuning Coil has been designed to 
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BRUNO RADIO CORPORATION 

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RADIO BROADCAST ADVERTISER 



75 




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THE 



GENERAL RADIO 

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In a search for an amplifier combination which would give the 
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While push-pull transformer coupling does not increase the ampli- 
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increased. The reason for this is that distortion due to tube over- 
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would be possible if the tubes were used as in other methods of coup- 
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A. C. filament supply is that hum voltages also cancel out, rendering 
the amplifier very quiet. 

The type 441 unit with two type 171 power tubes having a plate 
voltage of 1 80 will give more volume and better quality than a single 
transformer coupled stage using the type 210 power tube with 400 
volts on the plate. 

The General Radio Type 441 unit is completely wired and mounted 
(as illustrated) on a brass base-board with conveniently located bind- 
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with an existing set as a separate unit. 

The type 441 may be used with either the UX-226, UX-326, or 
UX-i/i, CX-37I tubes. 

Type 441 Push-pull amplifier $20.00 

The Type 441 unit is licensed by the Radio Corporation of America 
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Type UX-226 or CX-326 Amplifier Tube $3.00 

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GENERAL RADIO COMPANY 

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76 



RADIO BROADCAST ADVERTISER 




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I 



A KEY TO RECENT 
RADIO ARTICLES 

By E. G. SHALKHAUSER 

THIS is the twenty-fourth in stallment of references 
to articles which have appeared recently in var- 
ious radio periodicals. Each separate reference 
should be cut out and pasted on 4" x 6" cards for 
filing, or pasted in a scrap book either alphabet- 
ically or numerically. An outline of He Dewey 
Decimal System (employed here) appeared last in 
the January RADIO BROADCAST. 



R402. SHORT-WAVE SYSTEMS. SHORT-WAVE 

QST. July, 1927. Pp. 8-14. TRANSMISSION. 

"Short-Wave Radio Transmission and Its Practical 

Uses," C. W. Rice. Part i . 

The ionization of the atmosphere through cosmic radia- 
tion as well as through propagation of electron streams from 
the sun determines the nature of electromagnetic waves, as 
stated. How this ionization affects day and night and also 
seasonal variations is explained from experimental data 
obtained to date. Comparison is made between auroral 
phenomena and the theory of ionization as well as the effect 
of terrestrial magnetism on the motion of the electron. Skip 
distance effect is said to be due to the bending of the waves 
in the upper atmosphere, the degree of bending depending 
on the wavelength. 

Rjoi. 6. HIGH-FREQUENCY BRIDGE. BRIDGE, 

QST. July, 1927. Pp. 15-20. H iib- frequency. 

"A Bridge to Measure Capacity, Power Factor, Re- 

sistance, and Inductance," J. Katzman. 
The purpose of the article is to describe and explain the 

important factors of the Wien Series Resistance Bridge 

when used to measure C, L R and power factor accurately 

to i' of i per cent. 

R344J- TRANSMITTING SETS. TRANSMITTERS, 

QST. July. 1927. Pp. 24-28. Tuning. 

"Some Light on Transmitter Tuning," R. A. Hull. 
The construction of a shielded oscillator and its use in 
tuning transmitter circuits for good signal output are out- 
lined. Good plate and filament supply regulation is one of 
the main requirements. The proper method of tuning various 
circuits to adjust the wavelength of the oscillator and the 
antenna, and the correct amount of grid excitation to be 
used are told. Key thumps can be greatly reduced by having 
proper coupling and antenna tuning. 



SHORT-WAVES. 
Band," E. M. Guyer 



R402. SHORT-WAVE SYSTEMS. 

QST. July, 1927. Pp. 29-30. 

"An Investigation of the 5-Meter 
and O. C. Austin. 

Some problems on the construction and the operation of 
5-meter transmitters are related, photographs of several 
sets being shown with a list of material fortheii construction 
appended. 

R342. AMPLIFIERS. KEYING 

QST. July, 1927, Pp. 33-35. AMPLIFIERS. 

" Keying the Amplifier," A. G. Shafer. 
A keying system, whereby a specially constructed key is 
placed in the grid circuit of one of the amplifier tubes, is 
utilized to prevent key thumping. The system consists of 
changing the capacity of the coupling capacity to such an 
extent as to prevent proper transfer of energy from the 
oscillator without actually breaking any part of the circuit. 

R344-3- TRANSMITTING SETS. TRANSMITTER, 

QST. July, 1927. Pp. 36-40. Short-Wave. 

"A Constant Frequency Transmitter," W. H. Hoffman. 
A non-crystal oscillator, capable of maintaining a con- 
stant frequency output, yet flexible enough that the fre- 
quency may be shifted to other amateur wavelengths, is 
described and illustrated. 

R344.5. ALTERNATING-CURRENT SUPPLY. SOCKET POWER. 
Radio. July, 1927. Pp. 25-ff. "A B C" 

"ABC Socket Power For Large Tubes," G. M. Best. 
A discussion on the assembly and the operation of several 
combination ABC socket power units and the results ob- 
tained when used with a Browning-Drake receiver are given. 
The Raytheon 35O-mA. tube is used with each combination. 
All wiring details of the units, including those of the 
Browning-Drake receiver, are shown. 

Ri6o. RECEIVING APPARATUS. 



Radio. July, 1927. Pp. 29-ff. Single-Control. 

"Trouble Shooting the Single-Control " 
Gilliland. 



RECEIVER, 
glt> 

1 Set," M. P. 

In adjusting single-control receivers foi selectivity the 
following points are said to be of importance: Proper neutral- 
izing of all radio- frequency stages; balancing of tuned cir- 
cuits. For volume control a shunt resistance across the 
secondary of the first audio transformer is recommended. 

R3io. ELECTRON TUBES. ELECTRON 

Radio. July, 1927. Pp. 47-ff. TUBES. 

"Vacuum Tube Characteristics." 

The characteristics of dry cell tubes, power tubes, high-mu 
tubes, and special detector tubes, also of the new a.c. 
filament tubes such as the ux-226, the ux-28o, the i/x-^Si. 
the i x-}27, are given. The quadratron, the Kmerson multi- 
valve, the Sovereign A-C tube, the Van Home A-C tube, the 
new A-C Magnatron tubes and the Armor A-C 1 10 tube are 
described. 

Ri6o. RECEIVING APPARATUS. RECF.IVKK 

Proc. I. R. H. May, 1927. Pp. 387-395. MEASUREMENTS. 
"Notes on Radio Receiver Measurements," T. A. Smith 

and G. Rodwin. 

The comparison of radio receivers electrically involves 
the three main points: sensitivity, selectivity and fidclitv, 
a> ^;iU>d. The method of test and of making and interpret- 
ing the curves presented are outlined. 



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The Last Word in Radio 

Radio is an exact science. There is a right and a best way for every- 
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RADIO BROADCAST ADVERTISER 



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R 376.3. LOUD-SPEAKING REPRODUCERS. LOUD 

Proc. I. R. I'. May. 1927. Pp. 363-376. SPEAKERS. 

"Loud-Speaker Testing Methods," I. Wolff and A. 

Ringel. 

An electric oscillator method is used in obtaining quanti- 
tative measurements in testing loud speakers. The output 
of an oscillator, having a continuously variable frequency is 
fed to the loud speaker. The results are recorded on a re- 
volving drum mechanism. The curves, showing variation 
of sound pressure against frequency, reveal interesting 
characteristics, as explained. 



antenna operating at one of its harmonics. Short waves of 
2.66 meters were employed, and observations have been 
made with the grounded and the ungrounded antennas. 

The paper also gives the test results on a new wave pro- 
jector devised by the author with special reference to high 
angle radiation of short electric waves. 



R344-3- TRANSMITTING SETS. TRANSMITTER. 

Proc. I. R. E. May, 1927. Pp. 397-400. 
"The Tuned-Grid Tuned-Plate Circuit Using Plate-Grid 



Capacity for Feed-Back. A Derivation of the Condi- 
tions for Oscillation," J. B. Dow. 
Mathematical equations are developed showing the con- 
ditions required for oscillation in the tuned-grid tuned-plate 
circuit of a transmitter. 

Ri62. SELECTIVITY OF RECEIVERS. RECEIVERS, 

Proc. I. R f:. May, 1927. Pp. 401-423. Selective. 

"Selectivity of Tuned Radio Receiving Sets," K. W. 

Jarvis. 

The question of modern receiver design, incorporating 
selectivity, fidelity of reproduction, and adequate sound 
volume, is d-scussed. The resonance circuit and its require- 
ments are analyzed mathematically and curves presented 
bowing relation between amplification and electivity of 
radio-frequency stages. Discussing quality of reproduction 
ihe problem of regeneration, the phase shift of the side 
bands and the transient response of the circuit are mentioned. 

Ri 1 3.3. DIRECTIONAL VARIATIONS. TRANSMISSION 

Proc. I. K. E. May, 1927. Pp. 425-430. PHENOMENA. 

" Radio Phenomena Recorded by the University of 

Michigan Greenland Expedition 1926," P. C. Oscan- 

van. Jr. 

The experiences encountered by the writer when using 
short waves for transmission on Maligiak Fiord, North of 
the Arctic Circle, are related. It was loted that when at- 
tempting to receive signals from stations working on wave- 
lengths of 50 meters or below, complete screening was f- 
fected when the receiver was placed at the foot of a hill 
which is of a height greater than 17 degrees from the 
horizontal of the station. Photographs of the station are 
shown. 

R$oo. APPLICATIONS OF RADIO. APPLICATIONS, 

RAD.O BROADCAST. Aug. 1927. Pp. 199-202. Paper 

"Saving Paper!" J. Millen. weighing. 

The device illustrated and described consists of an 

oscillating circuit coupled to a tuned circuit, a thermal meter 

;ecording the deflection when in resonance. The material 

to be measured acts in the capacity of a dielectric, thus 

changing the frequency of the resonant circuit, this change 

being recorded on the thermal meter. 

R 1 34.8. REFLEX ACTION. REFLEX 

RADIO BROADCAST. Aug. 1927. Pp. 208-210. CIRCUIT. 
"Have You a Roberts Reflex?" J. B. Brennan. 
Improvements which can be made in the Roberts circuit 
consist in increasing the sensitivity and selectivity, improv- 
ing the quality of reproduction, making it more stable in 
operation, and increasing its volume. These changes are 
discussed in detail. 

R376-3. LOUD-SPEAKING REPRODUCERS. LOUD 

RADIO BROADCAST. Aug. 1927. Pp. 211-212. SPEAKERS. 
"The Balsa Wood Loud Speaker." 

Data on the assembly and the oroperties of the new Balsa 
wood loud speaker are given. The wood is obtainable in 
kit form, and by careful assembly of the parts a speaker of 
excellent reproducing qualities is said to result. Suggestions 
concerning changes and improvements are offered for those 
who experiment with this type of loud speaker. 

R344-3- TRANSMITTING SETS. TRANSMITTER, 

RADIO BROADCAST. Aug. 1927. Pp. 213-217. Short-Wave. 
"A Flexible Short-Wave Transmitter," H. E. Rhodes. 
The construction of a portable telegraph-telephone trans- 
mitter for short-waves, using tuned-plate tuned-grid circuit, 
is outlined, many data being given concerning the 
general characteristics of the circuit employed. The set 
operates between 7900 kc. and 2650 kc. (38 to ! 13 meters). 
A series of tests were carried on, the results of which are 
shown graphically and discussed in detail. These include: i, 
'I he effect of varying the grid leak resistance; 2, the effect of 
varying the resistance of either the tuned-grid or tuned- 
plate circuit; 3, the effect of varying the coupling between 
the plate and the antenna coils; 4, the effect of varying the 
plate voltage. 

R2oo. RADIO MEASUREMENTS AND STANDARDIZATION. 
RADIO BROADCAST. Aug. 1927. Pp. 224-226. TONE 

"Judging Tone Quality," E. H. Felix. QUALITY. 

The subject of distortion in radio receivers is discussed 
from the standpoint of the listener when trying to dis- 
criminate between good and poor tone quality. What is 
desired is faithful reproduction throughout, from micro- 
phone to loud speaker. Because of the importance of har- 
monics in distinguishing different instruments it is es- 
sential that frequencies up to 6000 cycles be reproduced. 
Sug^csiiqns as to methods which can be used in judging the 
reproducing qualities of receivers are offered. 

R22O. CAPACITY. CAPACITY MEASUREMENTS. 

RADIO BROADCAST. Aug. 1927. Pp. 227-228. 

"Condenser, Coil, Antenna Measurements," K. Henney. 

The measurements of variable and fixed condensers, dis- 
tributed capacity of inductance coils and of antenna capac- 
ity and inductance can readily be made with the aid of a 
calibrated modulated oscillator. Data for the use of this 
instrument and typical measurements are presented. 



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R}43. ELECTRON-TUBE RECEIVING SETS. RECEIVER 

Neutrodyne, AC. 

RADIO BROADCAST. Aug. 1927. Pp. 232-234. 

"Constructing a Five-Tube Neutrodyne," H. E. Rhodes. 

A shielded, two radio-frequency, detector and two audio- 
frequency tube neutrodyne, using the new a. c. tubes, is 
shown and details for its construction given. Great sensi- 
tivity. selectivity and ease of operation are claimed for this 
circuit arrangement. 



. ELECTRON TUBES. ELECTRON TUBES, 

RADIO BROADCAST. Aug. 1927. Pp. 238-^240. High mu. 
"Use of Tubes Having High Amplification." A. V. 

Lough ren. 

The amplification characteristics of high-mu tubes are 
treated. The discussion analyzes the frequency character- 
istics of each stage in a resistance-coupled amplifier and 
the choice of the amplification factor. Oscillographs and 
curves show the results to be expected. 

R27O. SIGNAL INTENSITY. SIGNAL INTENSITY, 

Radio News. July, 1927. Pp. 12-13. Broadcast. 

"The Service Area of a Broadcast Station," S. R. Winters. 

Results of measurements made with a loop test set by 

S- W. Edwards, radio supervisor of the 8th radio district. 

on signal strength from several broadcast stations, are 

given. These show to what extent steel buildings, static, 

electrical disturbances and other noises affect radio re- 

ception at a distance. The working standard of 10.000 

micro-volts per meter intensity was used to determine a 

reliable reception area about the station. 

R}-,2-7. AUDIO-FREQUENCY AMPLIFIERS. TRANSFORMERS 
Radio News. July, 1927. Pp. 25-ff. Coupling. 

"Why Loud Speaker Coupling Devices are Necessary," 

I. F. Jackowski. 

An explanation is given of the necessity of coupling the 
loud speaker to the audio amplifier through some coupling 
transformer and auxiliary apparatus, in order to bypass the 
direct-current component of the power tube output energy. 

R8oo. (535.3) PHOTO-ELECTRIC PHENOMENA. CRYSTALS, 
Radio News. July, 1927. Pp. 32-ff . Photo-electric. 

"Light-Sensitive Crystals, G. C. B. Rowe. 
The construction of simple light-sensitive cells, using 
ordinary metals such as copper, zinc, etc. or molybdenite 
and the substance selenium, is described. The numerous 
applications of such cells are mentioned and diagrams 
show how such cells may be used by the experimenter. 



ELECTRON Ti BES, 

High mu. 



R33O. ELECTRON TUBES. 

Radio News. July, 1927. Pp. 50-51. 

"A New Electron Tube," S. Harris. 

A tube haying a fourth element has been developed for 
use in circuits where objectionable feed-backs are en- 
countered. With the aid of the fourth element, known as the 
"shielded grid," the ejfectof plate to grid capacity has been 
eliminated. It is stated that the amplification obtainable 
wi.h this tube is as high as 200 per tube at 50 kc. 

R38?. i. SHIELDS. SHIELDING. 

Radio News. July, 1927. Pp. 52-ff. 

"The Effects of Shielding,' H. A. Zahl. 

The effect that shielding has on the electrical properties of 
circuits is discussed in detail, with curves shown, and the 
method of making the measurements is described. 

R2oi. FREQUENCY, WAVELENGTH FREQUENCY. 

MEASUREMENTS MEASUREMENTS. 

Exp. W reless (London). July, 1927. Pp. 394-401. 

"The Exact and Precise Measurement of Wavelength in 
Radio Transmitting Stations," R. Braillard. (Con- 
cluded). 

The description of the wavemeter is continued from the 
previous article and the method of standardization is out- 
lined. Its accuracy is said to be exceptional, transmitters 
being adjustable to a variation limit of To,3c5 of their wave. 



R 1 3475. SUPER-HETERODYNE. SUPER-HETERODYNE. 

Exp. Wireless (London). July, 1927. Pp. 402-411. 

"Design and Construction of a Super-heterodyne Re- 
ceiver," P. K. Turner. (Concluded}. 

In the last of a series of articles on the super-heterodyne 
the author discusses the intermediate stages of amplification 
and the low-frequency stages, and proceeds to give a de- 
tailed analysis of the actual construction of the set. 

R8oo (621.354). BATTERIES, SECONDARY. BATTERIES, 

Amateur Transmitter. April, 1927. Pp. lo-flf, Edison. 

"Edison Storage B Batteries," H. Rodloff. 
The construction of small Edison cells from standard parts 
is described. Considerable information as to their character- 
istics and their properties is related. 

R382. INDUCTORS. CHOKE 

Amateur Transmitter. May, 1927. P. II. COILS. 

"Radio-Frequency Choke Design," Wm. Zeidlik. 
In order to obtain maximum efficiency in the operation 
of any shunt-fed transmitter, properly designed radio- 
frequency choke coils are essential, as stated. The method of 
determining correct coils for such purposes is outlined. 

R8oo(62i.3i 1.7). RECTIFIERS. RECTIFIERS, 

Amateur Transmitter. May, 1927. Pp. 12-15. Electrolytic. 
"Electrolytic Rectifiers, Lead-Aluminum Type," J. E. 

Hall. 

The theory and the principle underlying electrolytic 
rectifiers is given. Information concerning the electrolytes 
used, the forming process, the heating of the cells and the 
capacity of the units constructed, is outlined in detail. 



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TRANSMITTER, 



Amateur Transmitter. June, 1927. Pp. y-ff. Short-Wave. 
"Master Oscillator Kinks," K. M. Ehret. 
The design and construction of a master-oscillator, power- 
amplifier transmitter, using two ux-2io tubes are outlined in 
detail. The circuit differs somewhat from the usual, but is 
considered to give very good results and a sharp signal when 
1 adjusted properly. Complete circuit diagram and list of 
"'parts are presented. 




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RADIO BROADCAST 



DECEMBER, 1927 



WILLIS KINGSLEY WING, Editor 

KEITH HENNEY EDGAR H. FELIX 

Director of the Laboratory Contributing Editor 



Vol. XII, No. 2 



Cover Design - - - - From a Design by Harvey Hopkins Dunn 

Frontispiece - Television Apparatus of a European Scientist 102 

Television in Europe William J. Brittain 103 

The March of Radio - - - An Editorial Interpretation 105 

How the Radio Commission Can Set Radio "Radio Industry" Standards 

to Rights Why the South Has Few Stations 

What Can the Commission Do? The New WEAF Transmitter 

$100,000 to Improve Broadcasting News of the Patent Field 

What to Tell the Consumer and Where The Month in Radio 
What Broadcasters Want 

Applications of the Four-Electrode Tube Theodore H. }Ja\\en 109 

The Phonograph Joins the Radio Set - ' ' i la 

Make Your Own Radio Picture Receiver - - Austin G. Cooley 114 

Beauty The Keynote in the New Radio Receivers 118 

What B Device Shall I Buy? Howard E. Rhodes 120 

Measuring the "Gain" of Your Radio Receiver Keith Henney 123 

Book Reviews . , , , j^ I ^ 

Inventions and Patents, Wright The Story of Radio, Dunlap 

Loud Speakers - 126 

Power Devices 127 

Facts About the Fada "Special" Receiver - John F. Rider 128 

Our Readers Suggest - 131 

How to Improve Your Old Receiver - Edgar H. Felix 133 

A Quality Five-Tube A. C. Receiver James Mil/en 135 

A New "TwO'Ten" Power Amplifier William Morrison 138 

The DX Listener Finds a Champion - - - John Wallace 140 

"The Listeners' Point of View" 

As the Broadcaster Sees It Carl Dreher 142 

Radio As an Electro-Medical Cure-Ail Piezo-Electric Control of Stations 

Some Catalogues The Small Broadcaster 

"Radio Broadcast's" Laboratory Data Sheets - - - - - 146 

No. 145. Loud Speakers No. r49. Circuit Diagram of an A.C. Audio 

No. 146. B Power Device Characteristics ^ Amplifier 

VT ..,-, . No. 150. Oscillation Control 

No. 147. Gain No. I 5 r. Single Control 

No. 148. An A.C. Audio Amplifier No. 152. Speech 

Manufacturers' Booklets Available - - - '152 

" Radio Broadcast's" Directory of Manufactured Receivers - - 154 

What Kit Shall I Buy? ' - - - - - - - 170 

From the Manufacturers '.' 174 



AMONG OTHER THINGS. . . 

"DROBABLY the most interesting article in this issue from 
*- the point of view of the experimenter is the constructional 
data and operating and assembly instructions on the Cooley 
"Rayfoto" radio picture receiver. By the time this magazine 
is in the hands of its readers, all the essential apparatus will be 
available on the market and nothing will delay the experimenter 
in his experience in this new field. RADIO BROADCAST is glad to 
forward the names of readers who are interested in receiving 
printed matter and late bulletins to manufacturers who are 
supplying the various parts for the "Rayfoto" apparatus. After 
the appearance of Mr. Cooley's November article, a great num- 
ber of our readers wrote us for this information which has 
been supplied. A letter should at once be addressed to the 
undersigned, asking for additional data in case you have not 
already written. 

V\ WASHINGTON is the center of interest these days, what 
* * with the International Radio Conference and the changes 
in the Federal Radio Commission. The death of Commissioner 
Dillon is a great loss to radio in the United States and it will be 
next to impossible to fill his place. The resignation of Com- 
missioner Bellows removes one of the ablest members of the 
Commission, but President Coolidge has filled his place through 
the appointment of Sam Pickard, former secretary to the radio 
body. Mr. Pickard is a likeable and able individual and we 
believe his appointment is a wise one. Carl H. Butman, of 
Washington, was appointed as Secretary to succeed Mr. Pick- 
ard. Mr. Butman has long served RADIO BROADCAST as its 
Washington news representative and we are indeed pleased 
that the Commission has so wisely chosen a man who knows 
radio problems so well. 

A WORD about the authors in this issue: William J. 
** Brittain is an English writer on radio and scientific 
topics who has just returned from a European trip to see what 
is being done in television. Theodore H. Nakken is a research 
engineer for the Federal Telegraph Company. He is a pioneer 
in photo-electric cell work and is unusually familiar with radio 
progress abroad. Austin Cooley, whose "Rayfoto" picture 
apparatus has attracted national attention, is a native of the 
state of Washington, received his technical training at M. I. T., 
and except for his trip in 1916 with the MacMillan Arctic 
expedition, has been in New York for the past four years. 
John F. Rider is a well-known New York technical writer who 
is at work on an interesting series of "fact" articles about manu- 
factured receivers. 

T^HE next issue will contain another story about the Cooley 
* "Rayfoto" radio picture system and its operation, as well 
as interesting data about push-pull power amplification. An- 
other of Mr. Rider's articles about manufactured receivers will 
be featured as well as a wealth of constructional matter. 

WILLIS KINGSLEY WING. 



Doubleday, Page & Co. 

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DOLJBLEDAT, <PAGE & QOMPA^Y, Garden Qity, He 

Copyright, 1927, in the United States, Newfoundland. Great Britain, Canada, and other countries by Doubleday, Page & Company. 

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IOO 



RADIO BROADCAST ADVERTISER 



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TELEVISION APPARATUS OF A EUROPEAN SCIENTIST 



HpH IS equipment constitutes the television receiver developed by M. 
1 Holweck, who is collaborating with Edouard Belin in the design of 
television equipment. M. Holweck is specializing in the receiving side of 
the installation. The received picture appears on the small circular screen 
at the top of the receiver shown in this illustration. Numerous other 
European scientists are devoting their time to the development of tele- 



vision schemes, and many and promising are the reports emanating from 
the various laboratories. M. Belin is, of course, a Parisian and has 
done most of his work in France. The short story which begins on the suc- 
ceeding page is from the pen of one who has visited many of the pioneers 
in the television field in Europe, and the information has, therefore, been 
obtained at first hand. 




VON M1HALY S TRANSMITTING APPARATUS 



TELEVISION IN EUROPE 



By WILLIAM J. BRITTAIN 




r HAT is Europe doing towards 
the furtherance of television? 
America already knows quite a 
lot about the work of Baird, and the public 
company formed to develop his machines 
has made his name known in most countries. 
But aside from this, little is known of the 
progress of the many experimenters in this 
fascinating art on the other side of the 
Atlantic. 

Recently the author went from England 
to find out what the Continental men are 
doing, what their apparatus is like, and 
whether they are preparing a surprise for 
the world, and in Berlin was found the man 
preparing the surprise. He is Denes von 
iYiihaly, a young Hungarian, and chief 
consulting engineer to A. E. G. (the General 
Electric Company of Germany). An 
engineer brought from America for the 
purpose is making a simplified version of 
Von Mihaly's apparatus to be shown in 
Berlin and London as a preliminary to 
forming television companies there. 

The vital feature of Von Mihaly's method 
is an oscillograph which consists of a 
tiny mirror mounted on twin wires. The 
mirror vibrates between two electro-mag- 
nets at speeds which sometimes reach 
thousands of times a second. Light re- 
flected from the object a face, a scene, 
or whatever it may be is focussed by a 
specially constructed set of Zeiss lenses upon 



the mirror. The mirror, vibrating rapidly, 
sees each point of the object in turn, in the 
manner necessary for television, and flashes 
it to a photo-electric cell. 

Von Mihaly has made his own cell, and 
it sends out currents corresponding ex- 
actly to the intensity of light or depth 
of shadow of each tiny point as it is 
reflected upon it. 

In his receiving apparatus Von Mihaly 
again uses vibrating mirrors. An electric 
lamp, shining brightly or becoming dim as 
the current from the transmitter is strong 
or weak, is concentrated by lenses upon 
mirrors which repeat the action of the 
mirror at the sender and zig-zag a beam of 
light over a ground glass screen. The vary- 
ing light beam, covering the screen eight 
times a second, makes up the picture. 

To ensure that the sending and receiving 
mechanisms are working exactly in time 
so that the mirror at the receiving end is 
shining light upon the centre of the screen 
at the same fraction of a second as the mir- 
ror at the transmitting end is "seeing" a 
bright part in the center of the object 
Von Mihaly uses a tuning fork arrangement 
on the same principle as those that have 
been used by experimenters in photo- 
telegraphy. A tuning fork in the receiver, 
kept vibrating by an electromagnet, acts 
as a switch, regulating current to other 
magnets which allow a wheel to progress 



one cog for every impulse, and so regulate 
the vibrations of the mirror. The apparatus 
at each end now fills a table, but Von 
Mihaly says he can simplify it to work as 
a home set in conjunction with a one-tube 
radio receiver. 

Behind this assurance is a secret. The 
secret is in a small black cylinder,' five 
inches by two and a half inches. The inven- 
tor calls it his "little black wonder." He 
will not tell the world what is inside, but 
told the author that with it it is possible 
to do away with the great amplifiers neces- 
sary in other systems. 

"Television sets for the home," he said, 
" will be simple and yet give a boxing match 
or a horse race. They will be sold in a few 
months for the equivalent of a hundred 
dollars." 

Von Mihaly has been working for thir- 
teen years on television. He first became 
interested when he was twenty, after hear- 
ing a lecture on photo-telegraphy by Pro- 
fessor Arthurn Korn. He carried on his work 
for the Austria-Hungarian government 
during the war, and on July 7, 1919, gave 
his first crude demonstration of television. 
Ministers in the laboratory of the Telephon 
Fabrik in Budapest then saw on a screen 
the images of the letters M. D. and REX 
transmitted from the young engineer's 
home laboratory in another part of the 
city. 



104 



RADIO BROADCAST 



DECEMBER, 1927 



It was the writer's privilege to be present 
at a recent demonstration of Mihaly's ap- 
paratus. The results obtained were con- 
siderably better than those of the earls- 
demonstrations referred to above, and the 
images were clearer than those seen by the 
author on Baird's screen. On the picture 
of a "televised" boy it was possible to see 
the collar, the wavy outline of the hair, 
the shape of the ear, the forehead, the 
eye, the nose, and the mouth, the latter 
merging'into shadow on the left side of the 
face. 

OTHER EXPERIMENTERS 

PROFESSOR Max Dieckmann, whom 
1 met in his station near Munich, 
Germany, has up to the present no result 
like this to show. He has achieved results, 
but has scrapped the transmitter and other 
apparatus that gave them. 

"I used mirrors," he told me, "but I 
came to the conclusion that no mechanism 
could ever be made light enough and ac- 
curate enough for television. I am therefore 
trying to make use of electrons. By two 
electro-magnets, alternated by currents of 
different frequencies, I make the stream of 
electrons or the cathode ray zig-zag 
over the object, and I am now experiment- 
ing with devices to register the result of 
this 'exploring.' 

"With electrons I think I have the real 
instrument for television. Electrons are 
almost weightless and can travel at any 
speed we need. All mechanism has a weight 
and inertia that in my opinion will always 
drag down efforts at perfect television. By 
perfect television I mean, of course, the 
reception of images as fine as published 
photographs. It is possible now to have 
crude television. You can have a picture on 
as large a screen as you like, but the larger 
the screen is the larger must be the patches 
making up the picture. Distance of trans- 
mission, too, offers little difficulty. We must 
concentrate on producing a finer image, and 
I believe electrons will enable us to do it." 

Professor Dieckmann is retaining his 




PROFESSOR MAX DIECKMANN 

former receiver which already uses elec- 
trons. The receiver is like a bottle. The re- 
ceived currents vary the flow of electrons 
from a tube fixed to the neck of the "bot- 
tle." By magnets similar to those in his new 
transmitter the varying flow of electrons is 
made to zig-zag over a screen at the bottom 
of the " bottle " which glows as the electrons 
touch it. When a strong current, showing 
that a light part of the object is being en- 
countered at the transmitter, sets off a 
heavy flow of electrons, the screen glows 
strongly at that part, and the glowing 
patches make up the picture. 

With Mr. Rudolf Hell, his chief assistant, 
Professor Dieckmann is working with en- 
thusiasm at his latest apparatus. 

Mirrors form an essential part of the 
apparatus of M. Edouard Belin, the scien- 
tist famed for his systems for photo- 
telegraphy, who has large stations at La 
Malmaison, near Paris. M. Belin inspired 
cartoons with a television machine thirty 
years ago. His latest apparatus looks 
businesslike. 




VON MI- 
H A L Y ' S 
TELEVISION 
RECEIVING 
APPARATUS 



Two rectangular mirrors, about half an 
inch long, set at right angles, are made to 
oscillate by cranks and connecting rods 
driven by an electric motor. A beam of light 
shines on the mirrcrs and is reflected zig- 
zag in the usual way. For his object M. 
Belin uses his hand. Light from the hand 
as the beam passes over it is caught by an 
eighteen-inch concave mirror at the bottom 
of a drum which concentrates the light on a 
photo-electric cell held by an arm half-way 
down the drum. With this apparatus, M. 
Belin told me. he can record fifty thousand 
flashes of light and shade a second. 

M. Holweck, collaborator with M. 
Belin, is responsible for the receiver. He has 
designed a special form of cathode ray 
oscillograph in which as complete a vacuum 
as possible is kept by an air pump, also 
of his own design. M. Holweck is working 
to perfect the fluorescent screen so that it 
will vary its glow exactly according to the 
strength of the stream of electrons. He has 
also made the apparatus more sensitive so 
that a difference of potential of five volts 
between the grid and the filament will ab- 
solutely cease the flow of electrons. This 
means that slight differences of light and 
shade in the object, and therefore, tiny 
differences in the current received, are re- 
corded on the screen. 

Promising results are being obtained. At 
present M. Belin is transmitting only the 
silhouettes of his hand. On the screen the 
outline of the hand can be seen clearly. 
The hand can be seen to move, and the 
fingers to bend. A silhouette of the profile 
of a face, and a simple photographic nega- 
tive, have been transmitted with equal 
success. 

"Our work is progressing gradually" said 
M. Belin. "We have found it better to pass 
over the object a bright spot of light rather 
than illuminate fiercely the whole object. 
It we used flood lighting to obtain the same 
brilliancy as our spot light gives us over a 
person's face the intensity would be insup- 
portable. 

" Earlier in the year we were sending over 
our object in a thousand points; now we 
have reached two thousand five hundred. 
We cover the object eight times a second 
which means that in our ordinary experi- 
ments twenty thousand signals are flashed 
a second. We are greatly encouraged by our 
present results. In a few months we should 
have something to offer the world." 

This is the stage European inventors have 
reached. Each one of them is watching care- 
fully every step forward by other workers 
and trying to go a step further. Von Mihaly 
is confident that all his system needs now 
is to be put on the market. Dieckmann and 
his young assistants are working quietly 
but eagerly. And all the time I was at the 
establissement Edouard Belin I was filled 
with the boyish enthusiasm which per- 
meates the atmosphere there. 

Of hopes and plans it would be possible 
to write pages but in this article an attempt 
has been made to keep plainly to facts to 
let America know just what Europe is 
doing in television. 



THK M 




NKWS AND IN rmPUH'ATIQN OK rilUUJ-'N T PAhlQ EVENTS 

How the Radio Commission Can Set Radio to Rights 



A THE peak of the radio season 
approaches, we look upon the situa- 
tion with considerable satisfaction. 
Last year, broadcasting was in chaos and 
the Radio Act had not been passed; this 
year, progress has been made in the di- 
rection of restoring order. Public interest in 
radio is at a maximum; the Radio Show at 
New York broke all records for attendance 
at an industrial exposition. Manufacturers 
and dealers report brisk sales. Broadcasting 
now has the stimulus of two competing 
chains. Everywhere there is activity and 
progress. 

The only sore spot in the radio situation 
is in the regulation of broadcasting. The 
Commission went about its task with dili- 
gence as soon as it was formed. It cleared 
the Canadian channels and put the stations 
back on even ten-kc. channels. Then it 
spaced the New York and Chicago broad- 
casters at fifty-kc. intervals, forcing time 
sharing in some cases to make it possible. 
After these commendable steps had been 
taken, the Commission confined its activi- 
ties to juggling a channel here and switch- 
ing a station there. 

We understood that the assignments of 
June 15 were merely an experiment, a stop- 
gap measure effective only until a compre- 
hensive plan of allocation could be worked 
out, which would mean an end to the 
heterodyne whistle. The persistently optim- 
istic announcements of the Commission that 
the broadcasting situation is now remedied 
give the impression that the Commission 
considers its major task completed. 

At the opening of the Radio World's 




Fair, Admiral Bullard pleaded for more 
time to give the Commission an opportun- 
ity to do its work; at the Radio Industries 
Banquet, he made numerous proposals to 
the radio industry, many of them no less 
than amazing, but nowhere have we had a 
simple, direct statement of the future plans 
of the Commission. Does the Commission 
consider its task virtually competed or 
will it devote itself to a radical improvement 
of broadcasting conditions? 

The Admiral's speech at the banquet 
contained some striking indications. Briefly, 
he stated that broadcasters should find a 
way to fix the responsibility for statements 
made in radio advertising; that direct ad- 
vertising stations should be taxed; that 
radio ought to be a public utility regulated 
by public service commissions; that pro- 
vision should be made to link up broad- 
casting for national sos calls, perhaps for 
such occasions as the loss of the President's 
racoon; that motors for electric elevators 
should be re-designed; and most ingenuous 
and amazing, that receiving sets should be 
equipped with crystals to permit of greater 
selectivity. 

A few words at the very end of this as- 
tounding speech were devoted to the Com- 
mission's plans. With regard to the high 
power stations serving the long distance 
listener, "the Commission is looking for- 
ward to a time when the listener, on any 
night of good reception, can hear broad- 
casting stations from the Atlantic to the 
Pacific, from Canada to Mexico, without 
interference, on channels cleared for them, 
not by arbitrary rulings of the government, 
not by fixed and necessarily discriminating 
classifications, but by the normal, logical 
process of demonstrated fitness and capac- 
ity to render a great public service. Such a 
development is entirely practicable on the 
basis of allocations now in force. It requires 
no sweeping changes, but only a clear pic- 
ture of the ideal to be attained, and a steady 
careful improvement of existing condi- 
tions. ..." 

Thus the ingenious Commission will by 
"orderly and natural, rather than by auto- 
cratic and arbitrary methods" bring us 



A RADIO TOUR OF THE CONTINENT 

Capt. L. F. Plugge, an English radio enthusiast, 
spent the months of July and August on a tour 
which the accompanying map shows. There were 
two radio-equipped cars, one of which is illus- 
trated. Each had a loop-operated super-hetero- 
dyne and a short-wave transmitter operating on 
6660 kc. (45 meters). Intercommunication was 
attempted and reception conditions along the 
route noted 



these ideal listening conditions. No one, 
unless it be the broadcast listener, will be 
imposed upon; only stations which elect 
by natural processes to eliminate them- 
selves will be taken off the broadcasting 
lists. 

The listener unless he lives within the 
shadow of a broadcasting station, that is, 
in that short distance which engineers like 
to call the service range, must put up with 
disagreeable heterodyne whistles. Only if 
we use "arbitrary" methods, which means 
actually applying the regulatory powers 
with which the Commission is endowed, 
can we hope for fewer stations. The natural 
tendency is toward increasing the number 
of stations and the power they use. The 
Commission leans upon a broken reed, if it 
expects "normal, logical processes" to 
eliminate stations. Rubber spine methods 
cannot help the broadcasting situation. 
There is only one solution, which we repeat, 
like Cato and his "Carthage must be des- 
troyed," and that is the elimination of at 
least four hundred broadcasting stations. 

What Can the Commission Do? 

ECTION IV of the Radio Act author- 
izes the Commission to classify broad- 
^^ casting stations, to prescribe the 
nature of service rendered by each, to assign 
bands and powers, and to determine the 
location of stations. There is no limitation 
on how far it may go in its work of classi- 
fication. 

Why does not the Commission use these 
powers? Why does it not classify broad- 
casting stations as (i) national, (2) regional, 
(3) local; divide the country into geographi- 
cal areas and prescribe exactly how many 




106 



RADIO BROADCAST 



DECEMBER, 1927 



stations of each class shall be licensed in 
each of those areas? 

Public convenience and necessity clearly 
establish the point that interference among 
stations should not be tolerated and cer- 
tainly the Commission should be competent, 
if it earns its keep, to determine how many 
stations of various powers will be accom- 
modated in the present broadcasting band. 
In fact, all of these points have been ana- 
lyzed for it by qualified experts in precise 
and unequivocal terms. 

NATIONAL STATIONS, to which exclusive 
channels should be assigned, might be de- 
fined as follows: (i) Power, 10,000 watts or 
over; (2) Service, fifty hours a week or 
more; (3) Location, at least ten miles from 
all centers of 100,000 or more population 
and at a point more than fifty miles from 
the nearest national station and not within 
200 miles radius of more than five national 
stations. 

REGIONAL STATIONS, sharing channels 
with other regional stations more than 
1000 or 2000 miles distant: (i) Power, 
2000 to 5000 watts; (2) Service, at least 
twenty-five hours a week, and (3) Location, 
not more than 100,000 population within 
a five mile radius, nor more than five re- 
gional stations within 100 miles. 

LOCAL STATIONS: (i) Power, between 250 
and 500 watts; (2) Service, at least twenty- 
five hours; and (3) Location, such that there 
are not more than five local service stations 
within a hundred mile radius. 

Such a program would, of course, require 
the elimination of stations in a few of the 



congested areas, a blessing to the radio 
audience. The stations so eliminated need 
not go out of business, but merely con- 
solidate with others serving the same area. 
Stations of less than 25O-watt power should 
be ruled off the air at once, not because they 
themselves contribute seriously to con- 
gestion but because their channels might 
better be assigned to national or regional 
stations. 

Concrete suggestions, which are not only 
logical, but also require the exercise of some 
of the "arbitrary" powers conferred upon 
the Commission by law, may be in order. 
We respectfully suggest the promulgation 
and actual observance of regulations for the 
accomplishment of four objectives, the con- 
stitutionality of which cannot be ques- 
tioned: 

i. ALL STATIONS should be required to 
adhere to their frequencies and those failing 
to do so, after occupying their assigned 
channels for more than thirty days, should 
be fined $500 for each violation noted, 
without any further consideration of their 
cases. The Commission has been buncoed 
by whining station managements into the 
belief that staying on a channel requires 
extraordinary equipment and engineering 
genius. A station failing to adhere to its 
channel is not technically competent and 
not worthy of a franchise on the air. 
Furthermore, after its fourth offense, a 
station's license should be cancelled, with- 
out further consideration of the case. The 
ether space thus regained should not be 
assigned to a new ether nuisance, but 




A COMPLETE RADIO INSTALLATION ON AN AIRPLANE 

Although the l/ille de Paris, the Sikorsky airplane built for Captain Fonck, the noted French flier, 
never started toward Paris, plans for the flight were exceptionally complete. Top right shows the 
small transmitter and a larger set below it. In the center is a regenerative receiver and at the extreme 
bottom, the antenna reel. The motor generator unit is at the extreme left and supplies plate current 
for the transmitter. The generator and propeller can be swung out through the fuselage when in use 



utilized in relieving congestion where it 
exists. The Commission's leniency with 
regard to channel wobbling, to which it 
attributes practically all heterodyning, is 
a remarkable example of unwarranted 
bashfulness and consideration the stations 
don't deserve. The five hundred dollar 
fine for each violation of the Commission's 
regulations gives the Radio Act plenty of 
teeth but, to our knowledge, the Commis- 
sion has never tried them out. 

2. THE COMBINATION and consolidation 
of broadcasting in congested areas should 
be encouraged by guaranteeing to the con- 
solidators the combined broadcasting priv- 
ileges of the stations so consolidated. For 
example, four, full time, 5OO-watt stations, 
combined into one, should be permitted a 
power increase to 2000 watts, or two, half- 
time stations, forming one, should receive 
full time. Furthermore, all local and re- 
gional stations, not sharing the same chan- 
nel, which combine, should be guaranteed 
privileged consideration on the basis of 
program merit, should they seek to secure 
full time on a single channel by challenging 
another station. 

3. POWER INCREASES to local and 
regional stations shall not be granted where 
congestion exists, unless other stations, 
having a power equivalent to the increase, 
be absorbed. Thus, for example, for a thous- 
and-watt station in New York to jump to 
1500 watts, it should be necessary for it to 
absorb a 5OO-watt station. 

National stations, on the other hand, 
serving large areas, should be encouraged 
to increase power, because they require 
clear channels and failure to employ the 
maximum power means that they are not 
making full use of the channel assigned to 
them. 

4. THE COMMISSION, empowered to 
assign hours of broadcasting to stations, 
should conserve ether space by limiting 
licenses only to hours actually used by the 
stations concerned. It has left problems of 
time division to the stations themselves, 
instead of utilizing its power to help in re- 
lieving congestions. There are many broad- 
casting stations which are assigned fifty per 
cent, of the time on a channel which use 
only ten per cent, of it, while the other sta- 
tion on the channel is required to remain 
silent, although it has program material to 
fill the unused time. In congested areas, the 
assignment of the time should be based 
upon the average hours which a station 
broadcast over the same period in the pre- 
ceding year. Increase over this time should 
be granted only upon the basis of program 
merit and service, or the unused time held 
to encourage consolidations and to accom- 
modate other stations. 

The present assignment of forty channel:- 
to New York and Chicago, nearly half the 
ether space in the eastern part of the United 
States, is an imposition upon the listener. 
Yet new stations are being licensed in New 
York and Chicago, although six stations in 
each of those cities have coralled ninety 
per cent, of the audience. This concentra- 
tion of broadcasting facilities in two centers 



DECEMBER, 1927 



DEATH OF RADIO COMMISSIONER DILLON 



107 



of population forces the rural listener to 
contend with heterodyning all over the 
dials and precludes power increases in rural 
areas where better and bigger stations are 
actually needed. 

The Federal Radio Commission has 
worked long and hard with its problem. 
It has done the best possible job without 
seriously disturbing or curtailing the priv- 
ileges of the broadcasting station owners. 
But, so long as it fails to regard its duty as 
serving the interests of the listening public, 
and fails to use the ample powers conferred 
upon it by the Radio Act to reduce the 
number of stations on the air, ether con- 
gestion will remain the unhealthy disease 
of the broadcasting situation. 

$100,000 to Improve Broadcasting 

THE National Association of Broad- 
casters appropriated the sum of 
$100,000 to make a scientific study 
of broadcasting. It plans to employ field 
engineers and program specialists to visit 
individual stations throughout the country. 
The procedure of the Association in the 
effective utilization of this fund has not 
yet been established. If it is sensibly ad- 
ministered, very valuable contributions 
can be made in the technical, economic and 
program problems of the broadcaster. 
From the technical standpoint, studio 
methods, as they affect transmission qual- 
ity, and the correct operation of the broad- 
casting stations to help in eliminating ether 
congestion are fruitful subjects for research. 
The Association might well help in de- 
termining just what the capacity of the 
broadcasting band is with regard to power, 
service range and geographical location of 
stations. 

In the field of program technique, critical 
study of the outstanding features and sys- 
tematic examination of voice and musical 
instruments which make good broadcasting 
could be very helpful. An investigation of 
the possibilities of building high grade 
programs by the use of recording methods, 
as suggested by Edgar H. Felix in a speech 
before the Association, might also be 
studied with a view to investigating its 
practicability. Mr. Felix suggested the re- 
cording of "scenes," blending the voices of 
speakers and pick-up music through mixing 
panels and the "editing" of programs much 
as films are cut and assembled, until the 
ideal feature is assembled. When thus worked 
over and perfected, it may be presented as 
often and through as many stations as its 
popularity warrants, without further cost 
for talent. This suggestion may result not 
only in better planned and coordinated pro- 
grams, but it may help to reduce the mount- 
ing wire costs which commercial broadcast- 
ers now meet. 

In the field of commercial broadcasting, 
a close study of the methods used to associ- 
ate the commercial program with the pro- 
duct of its sponsor and to secure the most 
effective results in a manner pleasing to the 
listener might help to increase the effective- 
ness of commercial broadcasting, an end 




Henry Miller 
THE LATE COL. JOHN. F. DILLON 

Colonel Dillon, member of the Federal Radio 
Commission from the Pacific Coast, died early in 
October. His loss will be keenly felt by the 
Commission and the radio world at large. A 
practical radio man of wide experience, Colonel 
Dillon had served in various technical capacities 
in the Signal Corps, and as radio inspector in 
charge of the Eighth District when headquarters 
were in Cleveland in 1913 and 1914. He was later 
transferred to San Francisco as Radio Supervisor 
for the Sixth District and it was from this duty 
that his appointment as a Radio Commissioner 
called him. His wide practical experience with 
government, amateur, and commercial radio 
made Colonel Dillon one of the most valuable 
members of the Radio Commission 

which is necessary to aid economic stabiliza- 
tion of broadcasting stations. 

The National Association of Broadcasters 
is to be commended for its foresight in mak- 
ing this substantial expenditure, which is 
likely to be returned many fold through 
better broadcasting and larger audiences. 

What to Tell the Consumer And 
Where 

ATLICTED with the expanded cran- 
iums resulting from mushroom 
growth, the larger manufacturers of 
the radio industry are often flattered into 
advertising excesses which ultimately cause 
financial embarassment. As typical of this 
trend, we received a dealer notice, not long 
ago, describing a new type of A, B, and C 
power device which was to make its debut 
to the world principally through three pub- 
lications having a combined circulation of 
over three million copies. Although a 
prophet is not often recognized in his own 
country, so frequently has the folly of plung- 
ing into expensive national mediums been 
demonstrated to the radio industry, that 
most manufacturers first make an effort to 
sell the merits of their products among the 
more influential radio listeners. 

The general public has been too fre- 
quently fooled by innovations to become 
immediate buyers through the medium of 
an advertising flash in national weeklies. 
They are inclined to consult the most ex- 
pert enthusiast whom they can reach before 
they are willing to risk their money on a 



device which may fail. The more successful 
manufacturers establish . their products 
among the more influential groups of radio 
buyers before they plunge recklessly into 
national campaigns in behalf of products 
which do not have behind them the weight 
of acknowledged approval of the better in- 
formed radio enthusiast. The influence of 
the radio enthusiast, like halitosis, is often 
the insidious element which prevents the 
success of the national advertising cam- 
paign which is not supported by the good- 
will of well informed broadcast listeners 
and constructors. 

WHAT BROADCASTERS WANT 

A LIST of hearings scheduled by the Federal 
Radio Commission early in October indi- 
cates the evils of requiring hearings upon all 
applications, regardless of their merit. For ex- 
ample, WBAW, Nashville, Tenn., a loo-watt sta- 
tion, operated by a drug concern, seeks to in- 
crease its power to 10,000 watts, making it 
necessary for nineteen stations to defend them- 
selves against this unwarranted incursion of 
their service range by the drug store carrier. 
There is no channel available for any new 
io,ooo-watt stations anywhere. 

Another hearing is demanded by WJBL of 
Decatur, Illinois, operated by a dry goods store, 
calling for a power increase which would damage 
the service of ten stations, including such widely 
recognized stations as WBAL and WJAX. 

WORD, the Peoples Pulpit Association in 
Chicago, seeks to occupy the channel of WTAS 
and WBBM, both well established and serving 
large groups. There is little question but that the 
defending stations will be able to show the Com- 
mission the presumptuousness of those demand- 
ing these hearings, but it is unfortunate that 
lawyers, witnesses and disorganization of station 
staffs are required to do so. 

"RADIO INDUSTRY" STANDARDS 

LJ B.RICHMOND, Director of the Engineering 
. Division of the R. M. A., perhaps inspired 
by our suggestions as to the desirability of one 
set of radio standards rather than two, in an 
article in the R. M. A. News, suggests that the 
R. M. A. and the N. E. M. A. should combine 
their work of writing radio standards. Although, 
as Mr. Richmond points out, the R. M. A. has 
ten times as many members as the Radio Divis- 
ion of the N. E. M. A., the long engineering ex- 
perience of the older organization and the great 
importance of the manufacturers comprising it, 
makes its cooperation in writing standards of 
vital importance. Mr. Richmond's fair exposition 
of the situation is a long step toward affecting a 
consolidation of the standards committees of 
both organizations, vitally necessary if either of 
them are to be in the least effective. 

WHY THE SOUTH HAS FEW STATIONS 

OENATOR Simmons of North Carolina re- 
J cently launched an attack upon the Federal 
Radio Commission, declaring that it showed 
favoritism to stations in the North. Illinois, 
Nebraska and Missouri, with a population of 
fourteen million, have more licenses to broadcast 
than the eleven states of the south with their 
population of twenty-seven million. 

The Senator is correct in his facts, but he dis- 
regards the point that the south has not been 
sufficiently progressive to erect its share of sta- 
tions with the consequence that the Northerners 
have already filled their wavelength bands. So 
long as the Commission disregards future needs 
by filling the ether bands with New York and 



108 



RADIO BROADCAST 



DECEMBER, 1927 



Chicago stations, there is not room enough for 
better broadcasting service in the more remote 
areas. 

HOW THE RADIO BEACON WORKS 

1'HE radio beacon operated at Hadley Field, 
New Jersey, the terminus of the New York- 
San Francisco air mail route, has proved re- 
markably satisfactory. Two directional antennas 
are used, set at right angles. By means of a 
mechanical keying device, the letter "A" (dot 
dash) is sent from one antenna and the letter 
"N" (dash dot) is sent from the second. The 
transmissions are so timed that the dots and 
dashes exactly interlock so that, at the points 
where the signals from both transmitters are 
received equally, a continuous dash is heard. 
That point of equal signal strength is exactly 
midway between the directional signals of the 
two antennas. The radio listener aboard the 
plane can determine from the signals he hears 
whether he is exactly on the course or to the right 
or to the left of his course, because, in the former 
case, he will hear the steady dashes, while off his 
course, he will hear either A or N, depending on 
whether he is to the left or the right of it. The 
closer to the landing field he approaches, the 
more narrow the midpoint at which the signals 
are heard to form dashes. A few hundred feet 
from the beacon station, a deviation of ten or 
twenty feet from the course is clearly indicated 
by the signal in the headphones. 

THE NEW WEAF TRANSMITTER 

IN SPITE of its 50 kw., the initial broadcasts 
of WEAF at Bellmore proved a disappointment 
to many New York listeners who have depended 
upon WEAF for their principal program service. 
There are large areas within twenty-five miles 
of New York which, due to the change of loca- 
tion, now receive a weaker signal from the jo-kw. 
transmitter than they did from the old 5-kw. at 
West Street. There have been other instances 
when the removal of stations, even a short dis- 
tance from the congested areas to permit increase 
of power, have actually reduced the number of 
persons served. 

The transmitting apparatus at Bellmore is the 
last word in perfected control. The operator in 
charge sits before his desk and manipulates a 
number of buttons controlling each operation in 
the station, which has the proportions of a fair 
sized power house. If one of the water-cooled 
rectifier, oscillator or modulator tubes burns out, 
a light indicates the faulty tube. Pressure of a 
control button takes it out of service and connects 
a substitute without interruption of broadcast- 
ing. 

The receiving set used to maintain the sos 
watch has a range of several thousand miles and 
will be used to advantage by WEAF'S operator. 
WEAF'S sos watches already have the remarkable 
record of being the first to hear sos calls in the 
New York area and notify naval and coast 
guards in one case out of each three and of hear- 
in the sos simultaneously with naval and coast 
guard stations in the same proportion. Most 
broadcasting stations continue blithely on the 
air through sos calls until the silence of the ether 
around them impresses them with the fact that 
there must be something wrong. 

NEWS OF THE PATENT FIELD 

CLEVEN claims of F. A. Kolster's patent 
*-< 1,637,615, were declared invalid in a decision 
by the Second Assistant Commissioner of Patents 
on the grounds that the applicant's combination 
claim to a radio compass having a coil form of 
antenna was not novel and was well known at the 



time the applicant entered the field, f t f THE 
PATENT Office Gazette mentions the following 
suits over radio patents: Westinghouse vs. 
Allen Rogers, Armstrong 1,113,149; Radio Fre- 
quency Laboratory, Inc. vs. Federal Radio Cor- 
poration, Warren patent 1,603,432. ? f I THE 
DUBILIER Condenser Company has filed against 
the Radio Corporation of America on various 
socket power patents, f f ? JOHN V. L. HOOAN 
filed against the American Bosch Magneto Com- 
pany, Stewart Warner Corporation, Freed- 
Eisemann, Freshman, and Splitdorf for recogni- 
tion of his patent 1,014,002, and also against a 
large department store for its sale of Crosley, 
Stromberg Carlson, Federal and Fada sets which 
he alleges infringe his basic patent. I f I A. H. 
GREBE and Company, Stewart-Warner, and the 
Consolidated Radio Corporation (Wells Gard- 
ner, Chicago and Precision Products Company, 
Ann Arbor, Michigan) are now R. C. A. licensees. 



The Month In Radio 



THE Eastman Kodak Company suggests 
that RADIO BROADCAST encourage the use 
of the term "phototelegraphy" rather than 
"telephotography" in referring to the radio 
transmission of pictures. "Telephotography" is 
used among photography experts to denote the 
taking of pictures over long distances by the use 
of special lenses, although Webster approves the 
use of the term to describe the transmission of 
pictures by radio or wire. Indeed, so extensive 
has been this latter use in scientific circles that 
it would require much more than the approval of 
RADIO BROADCAST to bring about a change in 
the accepted terminology. Perhaps a compromise 
may be suggested which may help to eliminate 
the confusion. Why not refer to telephotography 
in the sense of transmitting pictures by wire or 
radio, as "radio photography" or "wire phot- 
ography," as the case may be? Iff RADIO will 
perform a new feat in eliminating the isolation of 
explorers when the Army Signal Corps and the 
Pathe Company participate in their exploration 
of the Grand Canyon of the Colorado. The expe- 
dition will traverse the entire length of the canyon, 
taking moving pictures and collecting data of 
scientific and educational value. Accompanying 
the explorers will be a radio telephone trans- 
mitter which will be used to 
link them with broadcasting 
station KGO, from which 
reports will be broadcast 
through a chain of stations. 
The explorers will venture into 
dangerous and heretofore in- 
accessible parts of the canyon. 
Iff WE NOTE in the list 
of changes ordered by the 
Federal Radio Commission, 
authorization to move KFKX 
from Hastings, Nebraska, to 
Chicago, Illinois. KYW has 
shared its channel with KFKX. 
The result of the move is to 
give Chicago listeners the full 
use of the channel without 
increasing station congestion. 
Nebraska and the great open 
spaces, however, suffer a 
curtailment of broadcasting 
service, f f f KOIL is now 
transmitting its regular pro- 
grams on 491 o-kc. (61. 06 met- 
ers), as well as its regularchan- 
nel in the broadcasting band. 



KOIL is a member of the Columbia chain, f * t 
THE MACKAY Companies purchased the Federal 
Telegraph Company's communication system, 
according to a recent announcement. The Fed- 
eral Company's equipment consists of high pow- 
ered arc stations installed along the Pacific 
Coast for point-to-point service in California, 
Washington and Oregon, and ship-to-shore ser- 
vice on the Pacific, f f f WE ARE opposed to 
the radiation of the same program by stations 
covering the same service area. The listener is en- 
titled to as much variety as the congested ether 
permits and the employment of two channels to 
do what may be done effectively with one is a 
waste of ether space. This practice is frequently 
indulged in by chain stations. ? f f ANOVELUSC 
of broadcasting was employed by the United 
Gas Improvement Company of Philadelphia to 
warn its customers that gas service had been 
temporarily discontinued because of damage by 
an accidental blast. Undoubtedly, this prevented 
many accidents upon the resumption of service. 
f f I THE American Agriculturist should be 
able to write a volume on the service of radio to 
the farmer as a result of the contest which it 
recently announced. It offers not too large prizes 
to farmers writing the best letters on the service 
which radio renders them. There have been many 
instances of thousands of dollars of saving 
through weather and market information, f t I 
f f I BROADCAST LISTENERS in Germany now 
number 1,713,899, according to Wireless Age, an 
increase of 78,171 in a three months' period. 
t f f THIRTY MILLION dollars worth of radio 
apparatus was involved in international trade in 
1926, of which about thirty per cent, consisted of 
American shipments, twenty-five of German, 
and twenty per cent, of British. Exports from the 
United States decreased twelve per cent, in 1926 
as compared with 1925, but the figures for the 
first half of this year show a revival of business. 
During the first half of 1927, American exports, 
were $3,705,861, an increase of $450,000 over 
the same period for the previous year. Iff 
OUR BRITISH contemporary, Popular Wireless, 
made some measurements as to the radiation 
range of a two-tube receiver, consisting of one 
stage of r. f. and detector. The set was presum- 
ably a non-radiating one, but actually its radia- 
tions were readily heard at a distance of twelve 
miles, although but fifty volts of plate battery 
were used. The radiations were found to blanket 
an area of nearly two hundred square miles in 
which some five million people reside. 




A TUG CAPTAIN WHO CAN TELEPHONE FROM 
HIS BOAT 

More than forty British-Columbian tug-boats, used in towing 
lumber on the waterways, are equipped with 5O-watt radiophone 
sets, tuned to 1507 kc. (199 meters). The view above shows a 
Captain's cabin and the complete receiving and transmitting 
installation 



1T1-JT1C 1 17/01 TIC? 

UrUi JriJUil 




AN ENGLISH SHIELDED-GRID TUBE 

In England and on the Continent, four-electrode tubes have been available for 
some time. The original research is credited to Schottky in Germany and the 
"shielded-grid" tube which has recently appeared in this country is credited to 
Dr. A. W. Hull 

By THEODORE H. NAKKEN 



A REVIEW of the progress of receiver 
design, which is possible by turning 
over the advertising pages of some early 
radio magazines, would offer some surprising 
evidence. We would see that mechanical im- 
provements, refinements, and modern methods 
have been the cause of radical changes in receiver 
pattern, and have so simplified operation of 
tuning as to make the modern receiver seem 
as far in advance of its forbears as is the present- 
day automobile ahead of the automobile of 
fifteen years ago. Yet we would note that there 
has been no basic change in the type of circuit 
used. The regenerative receiver of ten years ago 
still stands unchallenged as a sensitive device for 
translating signals from a distant broadcasting 
station. 

In searching for the reason of this lack of 
change in circuit arrangement, it will occur to 
us that we have reached a limit, and that it is 
almost impossible to obtain greater amplifi- 
cation than the present-day receiver gives us. 
And this limit is easily located as lying in the 
inherent characteristics of the vacuum tube as 
manufactured to-day. Even with its better fila- 
ments and better all round design, the vacuum 
tube of to-day has exactly the same funda- 
mental characteristics as it had when first con- 
ceived and built as an experiment. It follows, 
then, that if any improvements in receivers are 
to be expected, such improvements will not be 
realized before radically improved vacuum tubes 
are made available. 

But if we boldly lay the lack of actual progress 
at the door of the commercial vacuum tube, we 
must state why the tube should be responsible 
and how its inherent faults can be eliminated. 
The indictment against the present-day vacuum 
tube covers in the main two points lack of 
amplification and the tendency to cause oscil- 
lations due to inter-element capacity. Another 
charge that may be brought forward is in- 
efficiency, but this is almost identical with its 
lack of amplification. How to improve these 
conditions seems at the present time more 
important than all other efforts combined to 
make better receiver circuits, and so we will try 
to indicate shortly why the vacuum tube is 
inefficient, and how we can largely do away with 
the inter-element capacity, so as to get better 
all around performance from any circuit. 

The ordinary vacuum tube contains three 
elements filament, grid, and plate. The fila- 
ment acts as a source of electrons when heated; 
the plate, by virtue of its positive potential, 
causes these electrons to be attracted to itself 
and thus establishes a plate current; the grid, 



interposed between filament and plate, governs 
the amount of electrons that can reach the plate, 
acting, therefore, as a controlling element of the 
plate current. The grid, generally being held at a 
negative potential, tends to prevent electrons 
from wandering away from the source (the 
filament). The plate attracts electrons only by 
virtue of its high positive potential, and over- 
comes the repelling effect of the grid. 



Space Charge 




Plate Field + 



"-GridField- 



FIG. I 



In the three element tube there are three static 
fields which govern the tube's functions. From 
this diagram it is seen that there are two negative 
fields, both of which impede the flow of electrons 
to the plate 

It is not only the grid that tends to repel the 
electrons emitted by the filament but this repel- 
lent action is also exercised by the electrons 
themselves. In fact, we may say that the fila- 



FOR the last four years, foreign radio periodi- 
cals have contained a wealth of articles on 
the advantages of the double-grid lube. These tubes 
are chiefly used by our foreign neighbors because of 
their economy, but it has been inevitable that these 
lubes should make their appearance in this coun- 
try. More than a year ago, two manufacturers 
brought sample double-grid tubes to the Laboratory 
but the time was not yet ripe for their general in- 
troduction. In April, 1926, Dr. A. W. Hull of 
the General Electric Laboratories described his 
"shielded-grid" tube in the Physical Review and 
on October ist the New York newspapers carried 
the announcement of the Radio Corporation that a 
"shielded" grid tube the ux-222 was 'in the 
process of commercial development and would be 
ready for the general public "some time in the 
future." Believing that our readers would be inter- 
ested in a review of important information on 
double-grid tubes, thefollowing article was prepared 
at our request by Mr. Nakken who is familiar with 
the use and operation of multi-grid tubes on the 
Continent. THE EDITOR. 



ment is surrounded by a cloud of electrons, which 
therefore constitute a negative charge, trying to 
drive the electrons back instead of allowing them 
free passage to the plate. See Fig. i. Hence the 
plate must not only overcome the effect of the 
negative grid, but it also must nullify the effect 
of this cloud of electrons, which generally is 
called the space charge, in addition to its duty 
to attract electrons and thus establish the plate 
current. 

There are two combined factors then which 
tend to retard the flow of electrons from filament 
to plate space charge and the grid, and both 
are counteracted by the plate potential. It 
follows that part of the plate potential is utilized 
only to overcome the repellent action of space 
charge and grid, and of course, as far as amplifi- 
cation goes, this part of the plate potential is 
virtually useless. We may then say that the 
statement to the effect that the tube is inefficient 
is proved, the more so when it has been estab- 
lished that, in most designs, only from 10 to 15 
per cent, of the plate potential is actually avail- 
able for the establishing of plate current, and 
the remaining potential serves the purpose 
indicated. 

We know that the space charge is virtually a 
constant and its effect is added to that of the 
grid effect. The space charge, having its sphere 
of influence much nearer to the source of elec- 
trons than the grid, is much more powerful in its 
action, and thus a variation in grid potential, 
while representing a comparatively large change 
of the grid action on the flow of electrons, is 
decreased in its effect by the fact that it repre- 
sents only a comparatively small change in the 
total sum of the retarding action of grid and 
space charge combined. Here again we may say 
that the tube is proved to be highly inefficient, 
but now in the sense that the presence of the 
space charge prevents the grid from being fully 
effective. 

It follows from the foregoing remarks that the 
main reason for the inefficiency of the vacuum 
tube may be sought in the presence of the space 
charge. In fact, if the latter were absent, we 
would need only a small plate potential to obtain 
the identical results as at present, with the 
additional advantage that the grid would be 
fully effective because the grid field would be the 
only factor governing the magnitude of the elec- 
tron flow to the plate, instead of only part of the 
sum of two factors, of which the second one, the 
space charge, is by far the greater. The truth of 
the matter is that, if only the space charge were 
absent, the grid effect would be from three to four 
times greater than at present, i.e., without any 



110 

further changes in the tube the amplification 
factor would jump from, say, 8 to 30, yet the 
internal impedance of the tube would remain 
the same 

THE FOURTH ELEMENT 

WHEN we consider the static fields present 
in the vacuum tube we will see that we 
can count three space charge, grid field, and 
plate field. The former two are negative while 
the latter is positive. The space charge, as we 
have seen, is a constant, or virtually so, and must 
be nullified by part of the positive plate field. 
If, then, a second positive field were introduced, 
nearer the filament, and thus nearer the space 
charge, a fairly low potential field would easily 
nullify the latter's effect. Obviously this can 
easily be done by a fourth element, which 
would, of necessity, be placed either between 
filament and grid, or between grid and plate. 
This element, however, should not obstruct the 
flow of electrons from filament to plate, hence it 
should be an open structure, and for this reason 
logically take the form of a very 
open grid. In this way the four- 
element (double-grid) tube was 
born. 

Let us consider for a mo- 
ment that such a grid is placed 
between filament and grid, 
as in Fig. 2. Due to the con- 
struction of the tube it is much 
nearer the filament than the 
plate, and as the influence of 
such a field is inversely propor- 
tional to the cube of the distance, 
it becomes apparent that, if this 
grid is placed at, say, one third 
of the distance between filament 
and plate, its field is 27 times 
more effective than the plate 
field. Thus, if in the ordinary 
tube 90 volts is used on the 
plate, approximately 3 volts would suffice on 
this fourth element to completely do away 
with the space charge effect. This, first of all, 
increases the percentage effectiveness of any 



RADIO BROADCAST 



Auxiliary Fiel' 
Space Charge-, 




- Plate Field + 



Grid Field - 



Auxiliary Field + 



Space Charge - 

FIG. 2 

When an auxiliary positive field is introduced 
into the tube, the negative field due to the fila- 
ment is overcome, leaving the total negative 
field (which is detrimental to the progress of elec- 
trons to the plate) in a much reduced condition 

potential change on the controlling element, the 
grid proper, so that we reach automatically a 
much higher amplification factor, and secondly, 



Milestones in Vacuum Tube Progress 



Edison discovered "Edison Effect" .... 
Fleming experimented with Edison Effect . 
Fleming patented the two-element rectifier tube 
DeForest added third element to Fleming valve 
Tubes used in transcontinental telephony . 
Radio telephony from Arlington to Honolulu . 
Introduction of "hard" tubes to general use . 

Appearance of thoriated filaments 1923 , 

General use of power tubes 1926 I 

Development of high-current low-voltage filaments 1927 I 
Development of shielded-grid tube 1927 \ 




FIG. 3 

This diagram is that of a single radio-frequency 
amplifier using a double-grid tube, the inner, 
grid being at a positive potential with respect to 
the filament. The grid-plate capacity remains 
unchanged 



makes it possible to decrease the plate voltage 
considerably, say to ten or fifteen volts, and still 
retain a tube of the same general characteristics 
as the three-element original. 

It should be noted here, that we have assumed 
that this fourth element is built into an ordinary 
tube. The result then is that we have not in- 
creased the capacity between the plate and grid, 
and thus have not increased the tendency of the 
tube to oscillate due to capacitive feedback. 
This is a very important consideration, because 
it is easy enough to build an ordinary three- 
element tube with as high an amplification 
factor, as is done with modern high-mu tubes. 
But the latter is accomplished by narrowing the 
grid, i.e., by increasing the plate-to-grid capacity, 
and hence such tubes are almost completely un- 
fit for radio-frequency amplification. In such a 
tube the tendency for capacitive feedback is 
increased tremendously, and this capacity affords 
an easy path for the signal potentials to escape 
via the plate and become ineffective. As will be 



DECEMBER, 1927 

seen in Fig. 3, there is nothing strange in the 
hookup of a four-element tube, the extra elec- 
trode being hooked directly to some part of the 
B battery. 

We will now consider the second possibility in 
construction, i.e., that of placing the fourth ele- 
ment between grid and plate. Of course it must 
take the form of an open grid, as its purpose 
again is only to create a positive field, to be used 
to nullify the space charge effect. 

Let us suppose that the tube is now so con- 
structed that this element is placed halfway 
between filament and plate, in which case it 
follows that its effect on the space charge is 
eight times greater than the same potential on 
the plate. If, then, normally the plate has a 
potential of 90 volts, a positive potential of 12 
volts will be equally effective when applied to 
the fourth element, so that once more the plate 
voltage can be decreased to, say, 22^ volts. Due 
to its open construction the positive grid offers 
no obstruction to the flow of electrons, and itself 
draws only a very small current. Once more we 
make the grid fully effective in 
its influence upon the flow of 
electrons, so that the amplifica- 
tion factor of the tube has been 
materially increased. 

But simultaneously we have 
attained another effect, which 
merits close investigation. The 
positive grid, being held at a 
constant positive potential by 
the expedient of connecting it to 
a point on the B battery, may 
be stated to be constantly at a 
certain potential above ground 
potential. But after all, it is 
grounded. As it is interposed be- 
tween plate and grid, it has the 
effect of splitting the capacity 
between these two elements into 
two capacities, in series as can 
be readily seen in Fig. 4, because it acts the 
same as if a grounded plate were inserted be- 
tween two condenser plates. And as its structure 
is very open, its capacity to each of the elements 



Hih 



1883 
1896 
1905 
1907 
1914 
1915 
1920 






THE "INNER WORKS' OF AN ENGLISH SHIELDED GRID TUBE 

One really ought to call them "shielded-plate" tubes, for the grid differs but little from that in 

ordinary tubes, while the plate is housed behind the shield. This illustration and that which heads 

this article are reproduced from Wireless World (London) 



FIG. 4 

If the outer grid of a double-grid tube is made 
positive, the resultant grid-plate capacity of the 
tube is greatly reduced. At the same time it is 
possible to build tubes with much greater ampli- 
fication factor. The plate-grid capacity is reduced 
owing to the fact that two "condensers" are 
now in series 

of the tube is very small indeed, smaller in fact 
than the capacity between plate and grid origin- 
ally was. As the two capacities are in series, the 
resultant capacity between plate and grid is 
smaller than either one of the two, and hence 
we have, in this particular construction of the 
double-grid tube, almost completely eliminated 
the plate-grid capacity, with all its baneful 
effects on receiver efficiency. 

Thus, this type of vacuum tube has even 
greater advantages than when the positive grid 
is placed between filament and grid. We have 
created a tube which is highly efficient as to 



DECEMBER, 1927 



APPLICATIONS OF THE FOUR-ELECTRODE TUBE 



111 




FIG. 5 

In this detector circuit the outer grid is positive, 
the inner grid biased negative to prevent over- 
loading 

plate potential, its amplification factor has 
been increased considerably, and the plate-grid 
capacity has been largely eliminated, so that 
the tube may be called self stabilizing. 

No wonder then that the European amateur 
uses these double-grid tubes quite extensively, 
for the upkeep of a small receiver with tubes of 
this kind is very economical. 

Let us for a moment imagine what can be done 




PLATE VOLTAGE 

FIG. 9 

Measurements made in the Laboratory of RADIO 
BROADCAST show that when the inner grid is 
positive, the mutual conductance of the tube 
may rise to as high as 800 while the plate im- 
pedance is 125,000 ohms, indicating a voltage 
amplification factor of 100. Plate voltage-plate 
current curves are shown here 

1 with tubes of this kind. In an ordinary receiver 
employing two r.f. stages we may be glad if we 

! get a voltage amplification of about eight per 

' radio stage, so that the total amplification before 
detection is only sixty four. With tubes of this 
new design, and an amplification factor of, say, 
25, we get an amplification before detection of 
625 under the same circumstances, and with 
less trouble, because the capacitive feedback is 
as much more easily controlled. 

An ordinary detector gives an additional 
amplification of about four, so that with the 
commercial receiver and ordinary tube the de- 
tector delivers a signal with a voltage amplifi- 
cation of about 250. The new tube as a detector 
would give an amplification of about 12, so that 
its signal would represent an amplification of 

I 7500 times after the two r.f. stages and this is 

I voltage amplification only. 
Due to this enormous amplification, the con- 
ventional condenser and grid leak should of 
course be discarded for a negative potential on 
the detector grid, as shown in Fig. 5, because 
otherwise the detector would surely be over- 
loaded. 

For audio amplification the type of double- 
grid tube used is almost immaterial, but as only 
the one type (with extra element between plate 
and grid) gives great advantage of decreased 
inter-element capacity, and thus will be employed 
in the r.f. stages, we may just as well use it for 
the audio stages too. With a good three to one 
transformer one stage will give us an amplifi- 
cation of about 90, so that the total reaches, 
after the first stage, 675,000, as against 



FIG. 6 

A transformer-coupled audio amplifier stage 

using a tube whose outer grid is positive to reduce 

the space charge and make the plate voltage 

more effective 

ordinary tubes, with the same transformer, 24 
for one audio stage and a total amplification of 
6000. One perceives that almost unlimited per- 
spectives in receiver design are opened up, that 



M 

H 

3 



RADIO BROADCAST 
LABORATORY 



UX-222 
Inner Grid- 22.5 




p - MS i 




/ 



1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.2 0.4 0.6 0.8 1.0 1.2. 
GRID VOLTS 

FIG. IO 

Grid voltage-plate current curves on the new 
ux-222 tube with the inner grid positive. Note 
that the grid voltage lines are only two tenths 
volts apart indicating a large amplification factor 

enormous volume may be expected, and distance 
undreamed of may be covered. 

A study of the diagrams will reveal that the 
tubes are hooked up almost in the same way as 
ordinary tubes, with the exception of the posi- 




PLATE VOLTAGE 



FIG. I I 

The most interesting curve of all the plate 
voltage-plate current data with positive outer 
grid. Note the negative resistance at low plate 
voltages, the rapid rise when the plate voltage 
equals that of the outer grid, and the very flat 
straight portion where the tube is ordinarily 
worked 



FIG. 7 

A resistance-coupled low frequency ampli- 
fier with the outer grid of the tube positive 

live grid connection. Figs. 6 and 7 show dif- 
ferent audio stage hookups. 

The names "double-grid" tube is in the 
author's opinion, a misnomer. Generally we call 
the controlling element the grid, and as the 
fourth element in no way serves as a controlling 
element, it should not be called a grid, but 
simply the auxiliary element, or fourth element. 
Others have called the peculiar action of the 
fourth element between grid and plate a shield- 




no V. 



FIG. 8 

The circuit of a special a. c. -operated double 
grid tube in process of development. 

ing one, and call a tube thus constructed a 
shielded grid tube. It will be perceived that there 
is a good reason for this name, because the grid 
is actually more or less shielded against the plate 
effect, causing it to be remarkably stable. 

EDITOR'S NOTE 

THE curves presented here were made in the 
Laboratory and show the interesting charac- 
teristics of the ux-222 the R. C. A. "shielded 
grid" tube. Followers of our tube articles should 
note the extremely flat plate-current plate- 
voltage curve indicating an impedance with 
the outer grid positive of about 650,000 ohms, 
the negative resistance or falling characteristic 
at low plate voltages, and the high amplification 
factor of 222 secured by multiplying the mutual 
conductance by the plate impedance. If it is 
possible to place a load in the plate circuit of 
this tube, say at broadcast frequencies, of 
650,000 ohms, a voltage amplification of 1 1 1 will 
result, compared with the usual amplification of 
about 10 for a single tube and its accessory 
apparatus. 

With the inner grid positive, the mutual con- 
ductance rises, the plate impedance falls, and the 
amplification factor drops to about 100. Under 
these conditions the tube can be used in a resist- 
ance or impedance coupled low-frequency 
amplifier. 

Experimenters will delight in this tube. Its pos- 
sibilities are many and diverse. It will not revo- 
lutionize the radio industry, newspapers to the 
contrary, nor will it produce an entirely new era 
in receiver design. 1 1 is just one more step toward 
the ultimate goal of what? RADIO BROADCAST 
will publish additional data as it is available on 
the use of tubes of this type. 



The PHONOGRAPH Joins 



By Way of Introduction 

\ JOT many months ago, Carl Dreher suggested 
1 ' in his department in RADIO BROADCAST, 
that a radio broadcast program was almost the 
most ephemeral thing in the world. Thousands 
of dollars are spent to engage talent, wires 
covering half a continent are hired, advertising 
is scheduled in newspapers, several studio re- 
hearsals are held, and finally the elaborate pro- 
gram is put on the air. For an hour it lasts but 
it can never be repeated. If you did not hear it, 
all the king's horses and all the king's men 
couldn't put it into your loud speaker again. 

If it is not possible to reproduce a complete 
radio program in one's own home, one can at 
least recreate the equivalent. A very great num- 
ber of well-known radio artists are regularly re- 
cording for each of the important phonograph 
companies. Their records electrically cut are 
available everywhere. 

These pages list a few of the records made by 
artists who are perhaps better known to the 
radio listener than to the average purchasers of 
phonograph records. Here are fine recordings 
made by the ' favorities of the Atwater Kent 
hour, and the famous artists of the Victor, 
Brunswick and Columbia hours. As for the jazz 
bands, the comedy duos, and other enter- 
tainers with a more local fame, they, too, are 
forever at your beck and call on the black discs. 

One of the most important advances made in 
recent years for which we must thank the 
scientists is the great progress made in the re- 
production of music and speech by electrical 
means. All radio folk know how audio amplifica- 
tion has been improved, what with new amplifiers 
of excellent characteristics, better loud speakers, 
and so forth. An equally important improve- 
ment has taken place in the phonograph field. 
Now the phonograph, with its electrically cut 
records and its acoustically excellent exponential 
horns or cone loud speakers, will rival the musical 
fidelity of the best radio receiver. 



NEW RECORDS BY RADIO FAVORITES 



Released Since September 



WHAT no WE Do ON A DEW-DEW-DEWY DAY 

Is IT POSSIBLE? 

THE TAP TAP 

IF I HAD A LOVER 

PRESIDENT COOLIDCE WELCOMES COLONEL LINDBERGH AT 

WASHINGTON, D. C., JUNE 11, 1927 PARTS i AND 2 
PRESIDENT COOLIDGE WELCOMES COLONEL LINDBERGH AT 

WASHINGTON, D. C., JUNE n, 1927 PART 3 
COLONEL LINDBERGH REPLIES TO PRES. COOLIDGE 
COLONEL CHARLES A. LINDBERGH'S ADDRESS BEFORE THE 

PRESS CLUB OF WASHINGTON. D. C , JUNE 1 1, 1927 
COLONEL LINDBERGH'S SOUVENIR RECORD Concluded 
CIRIBIRIBIN (WALTZ SONG) 
IL BACIO (THE Kiss) (ARIDTI) 
INDIAN LOVE CALL (FROM ROSE-MARIE) 
ROSE-MARIE (FROM ROSE-MARIE) 
OLD BLACK JOE (FOSTER) 
UNCLE NED (FOSTER) 
ACTUAL MOMENTS IN THE RECEPTION TO COLONEL CHARLES 

A. LINDBERGH AT WASHINGTON D. C., PARTS i AND 2 
AT DAWNING 
THE WALTZING DOLL 
KENTUCKY BABE 
MIGHTY LAK' A ROSE 
ANGELS WATCHING OVER ME 
CLIMBIN* Up THE MOUNTAIN 
SAM'S BIG NIGHT 
THE MORNING AFTER 
JUST LIKE A BUTTERFLY 
JUST ANOTHER DAY WASTED AWAY 
UNDER THE MOON 
SING ME A BABY SONG 
You DON'T LIKE IT NOT MUCH 
OH JA JA 



Shilkret-Victor Orchestra 
Kentucky Serenaders 
Kahn's Orchestra 
Shilkret and Victor Orchestra 

Hon. Calvin Coolidge 

Hon. Calvin Coolidge 
Colonel Charles A. Lindbergh 
Colonel Charles A. Lindbergh 

Bori 

Virginia Rea 
Murphy 

Tibbett 



Victor Concert Orchestra 
Vaughn De Leath 
Utica Jubilee Singers 

"Sam 'n' Henry" 

Franklyn Baur 
Marvin-Smalle 
Stanley-Marvin 
Vaughn De Leath 

The Happiness Boys 



20819 
20827 
35835 
35836 

35834 

1262 
4015 
1265 

20747 
20668 
20664 
20665 
20788 
20758 
20787 
20756 



Vidm 



The public has suffered rapid education. They 
have learned that faithful reproduction of the 
original is possible in radio sets and in phono- 
graphs alike. And if the growth of broadcasting 
were not enough to sharpen the interest in 
music of all kinds, the new phonographs and the 
new records have come along to broaden the 
domestic entertainment horizon. 

The radio receiver has taken its place as a 
musical instrument a medium of entertain- 
ment along with the phonograph and the piano. 
The radio set in the public consciousness is no 







A COMBINATION 
RADIO-PHONO- 
GRAPH FROM 
BRUNSWICK 

The Brunswick 
Panatrope.Radiola, 
model ijSC. This 
instrument con- 
tains a Radiola 28 
super-heterodyne 
receiver with en- 
closed loop, which 
can be controlled 
by the dial in the 
front of the left- 
hand panel. On the 
right is the Pana- 
trope and below it 
the cone loud speak- 
er working out of 
a ux-2io amplifier 
which is also the 
amplifier for the 
radio set. The in- 
strument, complete 
with all tubes for 
6o-cycle a. c. oper- 
ation lists at $i 150 



longer merely a scientific marvel and mystery. 
And since they are so closely related because of 
what they can bring to the home, the phono- 
graph and the radio set have been drawn closely 
together in association of ideas and in actual 
physical form. Those who wish to buy a combina- 
tion radio-phonograph can choose many fine 
models from five or six well-known manufactur- 
ers. Those who already have a radio receiver 
which they wouldn't trade for the royal throne 
of Roumania can make their audio amplifier and 
loud speaker do double duty in reproducing 
phonograph records or a radio program accord- 
ing to the whim of the owner. All one needs be- 
side a good loud speaker system is any kind of 
turntable which will twist the record at an even 
speed of 78 revolutions per minute, and a good 
electro-magnetic pick-up. And there are many of 
the latter on the market. 



FAVORITES IN CHICAGO 

"Sam 'n' Henry" Correll and Gosden who 
nightly disport before the twin microphones of 
WON and amuse countless WON listeners. Their 
verbal antics are embalmed on Victor records, 
listed above 




DECEMBER, 1927 



113 



the RADIO Set 



New Records by Radio Favorites 



SOMETHING TO TELL 

STOP, Go! 

I AIN'T GOT NOBODY 

ROODLES 

MY WIFE'S IN EUROPE TO-DAY 

A LITTLE GIRL A LITTLE BOY A LITTLE MOON 

BABY FEET Go FITTER PATTER 

SOMETIMES I'M HAPPY 

WHEN DAY Is DONE 

No WONDER I'M HAPPY 

AIN'T THAT A GRAND AND GLORIOUS FEELING? 
MAGNOLIA 

JUST A MEMORY (VOCAL CHORUS BY ELLIOT SHAW) 
OY BELLS (VOCAL CHORUS BY VAUGHN DE LEATH) 
OOH! MAYBE IT'S You {VOCAL CHORUS BY FRANKLYN BAUR) 
SHAKING THE BLUES AWAY (VOCAL CHORUS BY FRANKLYN BAUR) 
JUST A MEMORY 
MY HEART is CALLING 
No WONDER I'M HAPPY 
JUST ONCE AGAIN 

BABY FEET Go FITTER PATTER 

THERE'S ONE LITTLE GIRL WHO LOVES ME 

FANTASY ON ST. Louis BLUES 

PARTS i AND 2 

AIN'T THAT A GRAND AND GLORIOUS FEELING? 
I AIN'T THAT KIND OF A BABY 
LEONORA 
PARES! 

HERE AM I BROKEN HEARTED 
HAVANA 

(VOCAL CHORUSES BY FRANKLYN BAUR) 
SWANEE SHORE 
MEET ME IN THE MOONLIGHT 
Do You LOVE ME? VOCAL CHORUS BY F. BAUR 
HONEY VOCAL CHORUS BY VAUGHN DE LEATH 
AIN'T THAT A GRAND AND GLORIOUS FEELING? 
Vo-Do-Do-DE-O BLUES 
THAT SAXOPHONE WALTZ 

1 COULD WALTZ ON FOREVER WITH You SWEETHEART 
Gio-Ap, GARIBALDI 
OH! YA! YA! 

FOR THEE (POUR Toi) (GORDON) 
FROM OUT THE LONG AGO (STRATTON AND DICK) 
IUST ONCE AGAIN (CHORUS BY F. BAUR) 
LOVE AND KISSES 
ARE You HAPPY? 
GIVE ME A NIGHT IN JUNE 
SONG OF HAWAII 
HAWAIIAN HULA MEDLEY 
Two BLACK CROWS, PART } 
Two BLACK CROWS, PART 4 
MAGNOLIA 
PASTA FAZOO LA 
THE VARSITY DRAG 

(VOCAL CHORUS BY BAUR, JAMES, AND SHAW) 
DANCING TAMBOURINE 

GOOD NEWS (VOCAL CHORUS BY BAUR, SHAW AND LUTHER) 
LUCKY IN LOVE 



Shilkret-V'ictor Orchestra 
Coon-Sanders Orchestra 
Fry's Million Dollar Pier Orch. 

Vaughn de Leath 

Radio Franks, 
White and Bessinger 

Harry Richman 

Harold Leonard and His Waldorf- 
Astoria Orchestra 

Harry Reser's Syncopators. 

Franklyn Baur 

Ernie Golden and His Hotel 
McAlpin Orchestra 

Abe Lyman's 
California Orchestra 
Don Vorhees and His Earl Car- 
roll's Vanieties Orchestra 

Paul Ash and His Orchestra 
Leo Reisman and His Orchestra 

Cass Hagan and His Park 
Central Hotel Orchestra 

Harry Reser's Syncopators 
The Columbians 

Van and Schenck 

Art Gillham-The Whispering 

Pianist 
Billy Jones and Ernest Hare 

(Happiness Boys) 

Barbara Maurel 
Paul Ash and His Orch. 
Ipana Troubadours 
South Sea Islanders 
Moran and Mack 

Van and Schenck 

Cass Hagan and His Park 

Central Orchestra 
The Radiolites 
Fred Rich and His Hotel Astor 

Orchestra 




3590 Brunswick 



3605 

10780 Columbia 

io66D 

10830 

10890 

10870 
io68D 
10710 
1081 D 
10740 

1 4oM " 

10900 " 

10980 
n n D 

10940 " 

10920 ' 

11140 Columbia 

lloSD 



THIS RADIO PROGRAM IS RECORDED 

Colonel Lindbergh before the Washington 
microphones which carried his welcome-home 
ceremonies to the entire nation. Victor has made 
four excellent records from this event. 




FOR the first time, phonograph records of a 
radio broadcast program are offered to the 
public. Victor has the distinction of pioneering 
and they offer three double-face records of the 
national welcome to Colonel Charles A. Lind- 
bergh at Washington. On these three records you 
have the voice of President Coolidge, the inter- 
spersed announcements of Graham McNamee, 
a short address by Colonel Lindbergh, and his 
longer speech at the National Press Club. It's 
all there and if you close your eyes, it isn't hard 
to imagine that the events are just taking place 
the cheers of the crowd, the applause which 
interrupts the speakers, the blare of the bands, 
and the quiet unruffled voice of Lindbergh. 

The Victor Company arranged a direct wire 
from Washington, culminating in their studios 
through which their recording apparatus got the 
same program as each of the broadcasting sta- 
tions. The ceremonies were recorded on forty-six 
record surfaces and finally edited down to the 
six surfaces now available. It is a good job from 
any point of view and Victor is to be congratu- 
lated. It is time that some of the historic events 
which are being offered to the radio listener with 
impressive regularity were preserved in perman- 
ent form. The next offering will be a champion- 
ship fight, we suppose. 



GUESS WHO 

None other than Billy Jones and Ernest Hare 
known to Eastern listeners of WEAF on Friday 
nights as the Happiness Boys. Their songs are 
recorded by Victor and Columbia 



A PHONOGRAPH-RADIO 

COMBINATION FROM 

VICTOR 

"Automatic Electrola-Rad- 
iola No. 955" is what Vic- 
tor calls this beautiful 
instrument. Records are 
changed automatically and 
groups of 12 can be played 
without attention. 
An 8-tube super-heterodyne 
with enclosed loop operating 
entirely from the light sock- 
et through the power supply 
for the vacuum tube ampli- 
fier and the cone speaker 
used alike for phonograph 
and radio reproduction. The 
radio receiver panel can be 
used in three positions. List 
price, $1550 




THIS article is the third in the serifs explain- 
ing the use and operation of the Cooley " Ray- 
foto" picture receiving system. The Cooley ap- 
paratus was demonstrated in actual operation at 
the New York Radio show and attracted an as- 
tounding amount of interest. Governor Alfred E. 
Smith of New York, who made the opening address 
of the Show, transmitted a part of a picture of 
himself, reproduced by the Cooley system over wiz 
and other stations of the Blue network. Many of 
the readers of this article undoubtedly heard that 
interesting broadcast. The subject of radio photo- 
graph reception is so large that it can be discussed 
only in part on each article. Our readers are ad- 
vised to preserve carefully each of the articles in 
RADIO BROADCAST on this system, beginning i^itb 
the first story in the October, 1927, issue. Pictures 
will be sent by broadcasting stations, using their 
regular assigned wavelength, and no tuning changes 
in your present receiver are necessary. Readers are 
urged to write us their experiences with the con- 
struction of the recorder. The development of the 
Cooley "Rayfoto" system opens for the first time 
to the American experimenter an important "next 
step" in radio development. 

THE EDITOR. 



THE articles on the Cooley "Rayfoto" 
system in theOctober and November issues 
of RADIO BROADCAST explained how the 
system works, told something of the results to 
be expected, and gave some details regarding 
the operation of a picture receiver. This third 
article in the series gives some general and 
particular information about the system, and 
diagrams necessary for the construction of a 
Cooley receiver are also presented. 

Many of the units for use in the radio picture 
receiver have been especially designed for the 
purpose and therefore possess the necessary 
characteristics for good results. They have been 
designed to take care of the present requirements 
of the receiver and are so flexible that they will 
still be suitable for use as the system may be 
gradually developed. Considerable care has 
been taken in this matter so that it will not be 
necessary to scrap any of the parts as the natural 
development of increased speed of reproduction 
and better quality are consummated. The 
approved parts, which have all been carefully 
tested, are made under the Cooley " Rayfoto" 
trade mark. 

Arrangements are now under way to supply 
various broadcasting stations with phonograph 
records which will enable them to put Cooley 
pictures on the air. The radio editor of your local 
newspaper is the best source of information. 

The complete set-up for picture reception by 
means of the Cooley system consists of three 
distinct units the radio receiver proper, the 
amplifier-oscillator unit, and the printer as- 
sembly. The first the radio receiver should be 
capable of quality reproduction of radio pro- 
grams for if it falls down in this respect it will 
assuredly do so when called upon to detect and 
amplify the incoming modulated wave which 
has super-imposed upon it the audible note 
representing the picture being transmitted. 

Passing from the last audio stage of the re- 
ceiver proper, the "picture signal" is further 
amplified in the amplifier-oscillator unit and 
it then modulates the output of the oscillator in 
accordance with the modulation produced by 
the picture. The varying output of the oscillator 
is made to cause corresponding variations in the 
output of the corona coil, and thus the intensity 
of the needle point discharge is made to produce 
an effect on the proper tallying with the original 




By AUSTIN Q. COOLEY 



picture. The corona coil is included in the second 
unit although the actual needle at which the 
discharge occurs is naturally a part of the third 
the printer-unit. This third unit consists of the 
needle, the drum upon which the photographic 
printing paper is wrapped, and the mechanism 
which causes the drum to revolve. It is purchas- 
able as a whole, for there are few who possess 
the mechanical ability and facilities for the 
construction of such an intricate piece of mechan- 
ism. 

The construction of the amplifier-oscillator 
unit from the approved parts is a simple matter. 
Fig. I shows a suggested layout while Fig. 2 
is the schematic diagram. The following parts are 
necessary for this unit: 
TI " Rayfoto" Amplifying Transformer 
Ri Variable Shunt Resistance for Primary of TI 
R 2 2OO-Ohm Variable Resistance Capable of 

Carrying too Mils. 
Ra i2-Ohm Filament Rheostat, i-Ampere 

Capacity 

Rr "Rayfoto" Relay 
Tj "Rayfoto" Modulation Transformer 
Ca o. i-Mfd. Condenser 
Ri o.oi-Meg. Grid Leak and Mounting 
Ci, Q o.ooo5-Mfd. Fixed Condensers 
C 4 o.ooo5-Mfd. Variable Condensers. 



LI "Rayfoto" Corona Coil 

L 2 Radio-Frequency Choke Coil 

Si Filament Switch 

$2 Push Button or Special Switch 

Ji, J2, Js Double Contact Short-Circuiting 

Jacks 

R 6 Filament Ballast Resistance 
One Telephone Plug 
Milliameter, o-aj-mil. Scale 
Two Sockets 
Fourteen Binding Posts 
Base- Board 
Panel 
Brackets 
"Rayfoto" Printer Unit 

Although wide deviations from the layout 
shown in Fig. i are permissible, it is also quite 
possible that considerable "grief" will be experi- 
enced in many cases where original schemes are 
attempted. We therefore suggest that the home 
constructor follow our plan of layout and con- 
struction very religiously, at least on his first set. 
The photographs indicate very clearly the 
arrangement of the apparatus and the experi- 
enced home constructor should have little 
difficulty in putting the apparatus together. 

All but the radio-frequency circuits may be 
wired up in any convenient manner. We find 




PICTURES RECEIVED BY THE COOLEY SYSTEM 

These two photographs have not been retouched and were received at the demonstration at the 
New York Radio Show. Governor Smith, in his radio address opening the Show let radio listeners 
hear how his picture, above, sounded. The heading above shows Mr. Copley and a part of his appara- 
tus as set up in operation at the Show. Governor Smith's picture is on the receiving drum 



MAKE YOUR OWN RADIO PICTURE RECEIVER 



115 



that ordinary No. 18 rubber covered fixture wire 
is very easy to handle and makes a reasonably 
neat job. Each circuit should be properly tested 
out, as will be explained later, before the wires 
are laced up in bundles. The radio-frequency 
circuit should be wired up with considerable 
care, the use of bus bar wiring or rigid wires 
having a fair amount of spacing between them, 
being recommended. No particular care need be 
taken to prevent losses in the radio-frequency 
oscillator circuit. The secondary of the corona 
coil, and its lead to the corona needle, however, 



require very special attention. This subject will 
be covered in another paragraph. 

When the "Rayfoto" printer has been com- 
pleted and set up with all connections to batter- 
ies, proceed as follows for testing and adjusting: 

Place two 2O1-A type tubes in the sockets and 
see that the filaments are properly lighted and a 
good range of brilliancy is controlled by the 
rheostat, Rs, of the amplifier tube. With the 
input terminals open, plug a pair of phones in 
meter jack, J 2 , for the amplifier. Turn the fila- 
ments on and off a couple of times to see if the 



I MECHANICAL ' 
UNIT -*1 




5O 



- c 



34 67 08 O9 O10 
A + B- B+ 8+ B+ 
A.F use. Relay 
Booster 




FIGURE I 
The circuit diagram of the amplifier and oscillator is given in this figure 



RADIO BROADCAST Photograph 

THE PRINTER UNIT COMPLETE 

With its spring motor. If the user desires to use 

the motor in a phonograph which he already has, 

the illustration on the next page shows a special 

unit made for that purpose 

proper click is obtained in the phones. If it 
sounds satisfactory, plug in the milliammeter. 
If you find the milliammeter reading down scale, 
reverse the connections to it. Adjust the C 
battery until the plate current is a little less 
than one milliampere. The plate voltage on the 
amplifier should be about 180 volts and the C 
bias to bring the plate current down to I mA., 
will have to be around 22j volts. 

Now connect a piece of wire between the plate 
terminal of the a. f. amplifier tube socket and the 
B plus terminal of the modulation transformer T 2 , 
and connect the input of the amplifier to the out- 
put of the radio receiver. Tune-in any broadcast 
signal and watch the milliammeter to see if it 
varies in accordance with the incoming signal. 
The phones may be plugged into jack J 2 and the 
gain control resistance, Ri, varied to determine 
if the proper control is obtained. 

Now connect the lead from the corona coil to 



Input from 

radio receiver A Bat. 
r^~2 3^~4 



AMPLIFIER AND OSCILLATOR 

To trip magnet 
mechanism on recorder 

10 l'T~i2~~tt~14 



RECORDER 



Rubber bands holding 
paper around drum 




Box containing 
spring motor 



FIGURE 2 

The suggested layout of apparatus shown in this drawing may be followed when you construct your amplifier-oscillator unit. The various identifying 
letters 6n the parts refer to similar letters on the circuit diagram given in Fig. i. The lead from the corona coil, Li to the needle holder on the recorder 
should not be over three feet in length and should be supported where necessary by silk thread. The parts for the oscillator-amplifier unit can be pur- 
chased and then assembled at home, and no special precautions are necessary in constructing the unit. The wiring may be done in straightforward fashion. 
The corona lead is a No. 38 wire and should be carefully handled, otherwise it will break. If the lead is broken by accident, unwind about three turns from 
the coil to make a new lead. The record unit cannot be home constructed and must therefore be purchased as a complete unit. The recorder depicted in 
this sketch is a complete unit containing a spring motor. Ri and Rs, not a part of the early model illustrated, may be located at any convenient point ia 
the layout. A fixed condenser was used for 4 in the first model. It is preferable that it be variable as indicated above. 



116 



RADIO BROADCAST 



DECEMBER, 



the corona needle. Give this lead no more sup- 
port than absolutely necessary. If this important 
lead needs support, it should only be by suspend- 
ing it from small threads. The lead should be 
made as short as possible and in no case should 
be over three feet long. Place a small piece of 
Azo No. 4 photograph paper on the drum and let 
the needle rest on it. The paper may be held 
around the drum by means of two rubber bands. 

Disconnect the input of the amplifier from the 
radio receiver and connect the booster terminal 
to about 90 volts of battery. Cautiously plug the 
meter in the oscillator circuit jack, ]s. If the 
meter registers over fifteen milliamperes, the 
circuit is not oscillating properly. Adjust the 
variable condenser until the current is brought 
down to less than ten milliamperes. 

Now watch the point of the corona needle to 
see if a very small corona discharge takes place. 
If not, re-tune condenser C 4 . If this does not 
bring results, try the various taps on the oscil- 
lator coil. If you are still unable to obtain any 
visible corona, increase the booster voltage to 
about 150 and try the different taps again. It 
may be found that all the condenser capacity is 
required to obtain a discharge. The length of the 
lead wire should then be shortened or a small 
fixed condenser, of about o.ooo5-mfd., may be 
placed across the variable condenser. Only a good 
mica condenser should be used. If the discharge 
is strong enough to burn a hole in the paper, 
the booster voltage should be reduced. The taps 
should be tried to determine the best position 
of maximum discharge. 

With the printing circuit operating properly, 
connect the input to the radio receiver and tune- 
in any broadcast signal. Take off the short 
circuiting wire on the trip magnet switch termi- 
nals and allow the drum to revolve with the 
needle riding on the paper. If the trip magnet 
does not trip from the radio signals, release the 
drum by operating the switch, 82 across the 
relay circuit. Watch the needle point to see if 
the corona varies with the incoming signal. 

GENERAL HINTS 

A FTER the "Rayfoto" printer and recorder 
** are set up for operation, trouble may be 
experienced in many cases due to feed-back 
from the corona circuit about which considerable 
information was given in the November issue. 
This trouble will depend greatly upon the 
characteristics of the radio receiver. To help 
avoid it, the experimenter should provide a 
separate set of small 22j-volt B batteries for 
the printer. As an additional precaution, the 
printer and recorder should be placed at a con- 
siderable distance from the radio receiver, say 
eight or ten feet, if convenient. After the appa- 
ratus is set up and working properly, attempts 
may be made to reduce this distance. Also 
experiments can be made with the battery 
circuits to determine the feasibility of operating 
the radio receiver and printer with the same B 
batteries. The experimenter will be aided greatly 
by the use of low-resistance B batteries. The 
filaments of the tubes in the "Rayfoto" printer 
may be operated from the same storage battery 
used for the radio receiver. All the above pre- 
cautions should be taken to prevent feed-back 
before attempting to tune up the "Rayfoto" 
printer. If feedback still occurs after tuning up 
the printer, additional steps may be taken to 
suppress it. 

If there is any feed-back from the printer 
circuit, the discharge will be strong and con- 
tinuous. A high reading on the meter when no 
signals are coming in indicates feed-back. 

The last resort to prevent feed-back is to shield 
the printer circuit. The shielding should not be 
attempted before the unit is set up and ready 




RADIO BROADCAST Photographs 

THREE VIEWS OF THE AMPLIFIER-OSCILLATOR UNIT 

The upper view taken from the side, shows the home-made relay mounted on the front panel and the 
corona coil is in the foreground of the picture. The center view shows the front panel layout and a 

top view is given below 





MAKE YOUR OWN RADIO PICTURE RECEIVER 



117 




RADIO BROADCAST Photograph 

USING A PHONOGRAPH AND ITS MOTOR 

The printer unit depicted above is designed for use with any standard phonograph and utilizes the 
spring motor in the phonograph for the operation of the drum 



for operating because in many cases the shielding 
will do more harm than good if it cannot be first 
tested out in an experimental way. 

Due to the different characteristics of radio 
receivers, we cannot give information here that 
will cover every case. In general, the proper re- 
sults may be obtained by running very small 
gauge grounded wires parallel to the corona feed 
wire and separated from it by a number of inches. 
This may necessitate re-tuning the oscillator 
circuit. Experiments with shield wires and 
shield plates will eliminate feed-back in most 
cases. 

In many cases it will help matters to adjust 
the neutralizing on the radio receiver or slightly 
de-tune one stage of radio-frequency amplifi- 
cation. 

With the printer circuit working properly, we 
may now adjust the relay and trip magnet. Ad- 
just the relay contacts so that they close before 
the armature strikes the magnet pole. With the 
contacts closed, you should be able to slide a 
piece of thin paper (the thickness of this page) 
between the pole and armature. The gap be- 
tween the contacts when open should be equal 
to two thickness of the paper used on the cover of 
this magazine. If sparking is bad, it may be neces- 
sary to increase this slightly. A condenser across 
the contacts will do more harm than good as it 
will cause the contacts to stick unless the spring 
tension is excessive. 

\\ith the trip magnet contacts open, adjust 
the C battery so that the plate current of the 
amplifier is about five mils. Adjust the spring 
tension of the relay so as to barely hold the 
contacts open with the five mils, in the circuit. 



After this adjustment is made, return the C 
battery adjustment to its original point. 

The voltage for the trip magnet should be 
as small as practical, consistent with strong 
operation of the magnet. The power for this 
magnet may be taken from the batteries operat- 
ing the radio receiver if small batteries are used 
for the printer circuits. 

W : ith all the foregoing adjustments and tests 
made, the experimenter is ready to test his set 
out on picture signals. It is well to have the 
developer and fixer solutions made up in advance 
although it will not hurt to let the undeveloped 
picture stand for a considerable time if the paper 
is protected from light. Instructions will be 
found on the developer tubes and fixing powder 
cartons for making up the solutions so we will 
not cover that information here. Regular trays 
for the solutions should be used for the sake of 
convenience although any enamel or glass tray 
or dish will serve the purpose. In mixing up the 
solutions, it will do no harm if they are made a 
little more concentrated than the manufacturers 
specify, using about 6oz. instead of Soz.of water. 

With the trip magnet properly adjusted, the 
speed of the drum should be adjusted and 
checked by counting the number of revolutions 
of the drum. If a converter drum speed of 100 
r.p.m. is used, the recorder drum speed should 
be about 105 r.p.m. The clutch should be free 
enough on the first tests so that the turntable 
will revolve with the drum in its locked position. 
By loosening up on a set screw on the collar 
directly below the spring, the clutch friction may 
be regulated. 

To receive a Rayfoto picture, tune-in signals 



from the station transmitting the signals so that 
they are received with maximum intensity. If 
the meter in the amplifier circuit runs up over 
fifteen mils, on the strong signals, reduce the 
intensity by the volume control on the radio 
set or the gain control on the printer amplifier. 
In most cases it will be good practice to reduce 
the radio-frequency input to the detector circuit. 

The minimum signal should be between one 
and four milliamperes. Adjustment of the mini- 
mum signal is more important than that of the 
maximum for if the minimum is too high, it will 
operate the relay when it should not, and if too 
low, it will cause irregular relay operation. 

While the synchronizing pulse is being trans- 
mitted from the station sending pictures, the 
drum should revolve and trip regularly with 
only a brief period of rest or lap. By regulating 
the speed of the driving motor the lap can be 
regulated. If the lap should be very long, you 
will find that the speed is too slow and that the 
drum is tripping only on every second synchron- 
izing impulse. Increase the speed. 

After the drum is adjusted to trip regularly, 
a "range" should be taken: that is, the signal 
should be increased to the point where the relay 
trips from the minimum rather than the syn- 
chronizing signal, and then the signal should be 
decreased to the point where the relay does not 
trip at all. The operating adjustment should be 
about half way between the two points. The 
operating range of the relay should be as large 
as possible. If it is very small, it may be in- 
creased by increasing the amplifier tube's C- 
battery potential so that the plate current is 
practically zero when no signals are being re- 
ceived. 

When the synchronizing adjustments are 
made and the paper placed on the drum, you 
are ready to start as soon as the picture signals 
begin. The paper should be drawn up to fit the 
drum tightly. If the center of the paper at the 
lap bulges out very far, a rubber band may be 
placed around the center of the drum and slid 
along when the needle approaches it. Care should 
be taken not to get the hand close enough to_the 
corona feed wire to detune the circuit. 

After the picture is received the paper is placed 
in the developing solution until developed to the 
proper density. It is then dipped in the washing 
bath and placed in the fixing solution. After 
remaining in the fixing solution for ten or fifteen 
seconds, it may be removed temporarily for 
observation purposes but should be replaced in 
this solution for ten or fifteen minutes and 
washed in running water for five or ten minutes, 
if it is desired to preserve the picture indefinitely. 

In some cases the experimenter will experience 
excessive blurring, lack of detail, streaks in the 
pictures, improper contrast, etc. In the next issue 
of RADIO BROADCAST we will give more complete 
information that will enable the experimenter to 
clear out any such troubles should they arise. 



The Freedom of the Air 

EXCERPT from a news item in the New 
York Times of May 3, 1927, under the 
caption, "Pacifist Talk Hushed by Radio 
Station WGL:" 

"We are proud that Mrs. Corson is a woman," 
Mrs. Ford said, "proud that she comes from 
Denmark, that country which upholds an ideal 
of peace, that country which said to the enemy, 
"If you must cut through our country, even if 
you must cut through our women and child- 
ren" 

At this juncture Mr. Isaacson cut out the mi- 
crophone through which she was speaking and 



substituted one in the studio through which 
music was broadcast as a stopgap. 

Mr. Isaacson later explained to the radio aud- 
ience what had happened. In discussing the in- 
cident later he said: 

"We believe in free speech and I have always 
been willing to extend the use of our station to 
anyone to express his views, but there are certain 
things which are dictated by good taste. This 
was not the time nor the occasion for such a 
speech." 

Excerpt from a news item in the New York 
Sun of July 18, 1927, under the caption, "Worm 
Controversy To Be Aired from WGL:" 

Fred B. Shaw, one time international fly fish- 



ing champion, will have an opportunity to dis- 
cuss President Coolidge and his angleworm 
fishing to his heart's content to-night when 
WGL will allow him to broadcast, uncensored, his 
speech which was barred last week by another 
station. 

"Our broadcast policy has always upheld free 
speech on the air," declared Dr. Charles D. 
Isaacson, program director of WGL, in extending 
the invitation to Mr. Shaw yesterday, "and for 
that reason we are only too happy to extend the 
privileges of our broadcast station to you." 

A vexing question is thus cleared up for all 
time. What is free speech a la Isaacson? It is 
freedom to discuss angleworm fishing. But not 
to discuss war. 



Beauty the Keynote of 




AN INSTALLATION that is completely self- 
rv contained the Bosch Model 57. Although there 
is a very efficient loop built in, provision has been made 
for the use of an outside antenna where desirable. The 
receiver employs seven tubes, and is tuned by a single 
main dial. A cone loud speaker is harbored within the 
cabinet. Price, $340. For power operation, $100. extra 






'T'HE set builder can now obtain a cabinet for his receiver which is 
* every bit as beautiful as those which house the most exjMMisive of 
factory-built receivers. The Model 80 cabinet of the Musical Products 
Distributing Company, New York, here illustrated, is in combination 
walnut and su tin wood. The set compartment measures approximately 28 
inches long, 10 inches high, and 15 inches deep. Price, $250. 



118 



the New Radio Receivers 



Making the Most of 
Surroundings 

It is easy enough to discuss the 
offerings of the current radio season 
abstractly but one should visualize 
this year's radio sets in the proper 
domestic surroundings to appreci- 
ate what great strides have been 
made toward making radio a truly 
domestic bit of furniture. The illus- 
trations on these two pages show 
radio equipment in home settings 
and who will deny their grace? 






I 





AN INTERESTING design in loud speakers, the new Amplion 
- r - "Fireside." This loud speaker has a large cone mounted on a big 
sound-board, exceptional fidelity of reproduction being possible. The 
screen stand and long cord render the "Fireside" readily portable, 
making it easy to plure the loud speaker uny where in the room or out- 
side on the porch. The panelling is of embossed walnut, attractively 
curved, combining a grille front and bark. The height is 36J inches, and 
the cone is 16} inches. Price, $97.50, with 20-foot cord 



ATYPICAL example of the trend of the more expensive radio receiver, 
in which utility and beauty are in combination. We are taken back 
by this Wiiithrop secretary to America's younger days, when money was 
scarce and furniture was made to serve dual purposes. Nowadays a return 
to this state of affairs is demanded since home space is so scarce. The radio 
receiver built into the Winthrop is the popular Splitdorf single-control 
six-tube set. The price, complete with power operation and loud speaker, is 
$600. 



119 




By HOWARD E. RHODES 



f If ^O WRITE of B power units in general 
I terms, with the object of assisting in their 
^ wise selection, is not difficult because there 
are simple rules that can serve to guide the pros- 
pective purchaser. In the first place it should be 
realized that the satisfaction which any power 
unit gives in service frequently bears a close re- 
lation to its cost, for power units can be built 
to meet almost any price. Cheap units, con- 
structed of inferior materials, are often capable 
of giving as good results as more expensive de- 
vices, during a single demonstration, but whether 
the cheaper device will stand up for as long a time 
in service is certainly open to question. 

The first rule in the purchase of a B power 
unit should be insistance upon a well-known 
make, purchased through a reputable dealer, 
for only from such a source can you be assured 
of obtaining satisfactory service. One of the sim- 
plest and most satisfactory methods of apprais- 
ing a B power unit to make certain that it will 
satisfactorily operate your receiver, is to give it a 
trial lasting several days in your own home, un- 
der actual working conditions. Only a reputable 
dealer selling a good product can afford to do this 
for you. A cut price dealer, with little or no in- 
terest in his customer once the sale has been 
made, cannot afford to sell a unit to you on the 
basis of a trial lasting several days. The unit 
purchased from a reputable dealer might cost 
somewhat more, but the higher price is justified 
because of the better service and greater assur- 
ance of satisfaction which you can obtain. 



There are many things about a B power unit 
which must be taken more or less on faith. 
You can't tell, by looking at the device, what 
kind of chokes are used or if the condensers in 
the filter circuit have a sufficiently high voltage 
rating so as to prevent any possibility of break- 
down. Then again, the design of the transformer 
supplying the rectifier and filter circuit is some- 
thing that cannot be examined when you buy 
the unit. It is only by relying upon the reputa- 
tion of the dealer and of the manufacturer whose 
product he sells, that you can have any assur- 
ance of a properly designed unit. If care is taken 
in the selection and use of a B power device, it 
will give satisfactory operation and lasting 
service for years. 

In the list appended, we have given the im- 
portant characteristics of about twenty-five 
well-known B power units. Since there are being 
made at the present time about one hundred and 
thirty of these units, it will be seen that the list 
is by no means exhaustive. 

The proper selection of a B power unit is a 
matter of knowing the total plate-current drain 
of the receiver and of then finding a device that 
will supply the correct voltages to your receiver 
at this current drain. You must make certain 
that the maximum voltage available from the 
device when supplying a milliampere load equal 
to that of your receiver is sufficient to supply the 
power tube you are using. The maximum output 
voltage of the device should be 180 volts, or 
slightly more if a 171 type tube, with 40.5 volts 



grid bias, is used in the output ; if a 112 type tube 
is used, with 9 volts grid bias, the maximum volt- 
age should be about 135 volts. The information 
given in the appended list includes the maximum 
output voltage which the units will supply at 
various current drains. 

Of course, it is also essential that the power 
unit be capable of supplying the other tubes in 
the receiver with the voltages they require. 
These voltages are obtained from voltage taps 
on the power unit and in most cases the voltage 
that is obtained from any one of these taps varies 
with the current being drawn from it and the 
other voltage taps, and for this reason it is not 
possible to give any definite figures for the volt- 
age output from these taps. Many power units 
use adjustable or semi-adjustable resistances so 
that the desired voltages can be obtained by 
proper adjustment of the resistance. These re- 
sistances should not be adjusted by guess but 
should be adjusted with the aid of a high-resist- 
ance voltmeter. This is a service any reliable 
dealer can give you. 

There are some power units (those using glow 
tubes) which give practically constant output 
voltages independent of the load. If such a unit 
is purchased it may be connected to any receiver 
with assurance that the actual voltages being 
supplied to the receiver will be near enough to 
those marked on the terminals of the power unit 
for satisfactory operation. 

As will be seen in the accompanying list, some 
of the devices have been approved by the Na- 



DECEMBER, 1927 

tional Board of Fire Underwriters and many of 
the other devices have been submitted for test 
but have as yet not been approved. The sub- 
mission of B power units to the National Board 
of Fire Underwriters for their approval is a dis- 
tinct step in the right direction. It gives the pros- 
pective purchaser the assurance that the unit 
conforms to definite standards designed to make 
certain that the operation of the device will be 
entirely safe. 

The power input to a power unit is a measure 
of the cost of operating the unit. The input power 
to the average B power unit is about 25 watts, 
which is the amount of power required by a 
small electric light bulb. If we obtain power from 
the electric light company at the rate of ten cents 
per kilowatt hour, it will cost just about one 
quarter of a cent per hour to operate the average 
plate-supply device. To this cost of operating, 
we should, of course, add depreciation on the 
unit and the cost of tube renewals which must 
be made on an average of once a year. 

All B power units for use with an alternating- 
current supply must use rectifiers of some sort. 
A majority of units use a tube for this purpose, 
but there are also quite a large group that use 
electrolytic rectifiers; thousands of B power 
units using either type of rectifiers have given 
satisfactory service. When purchasing a power 
unit avoid those using unknown makes of rec- 
tifiers. Whether you purchase a power unit 



WHAT B DEVICE SHALL I BUY? 



121 




current and delivers a steady fluctuating direct 
current to the output terminals of the device. 
Some power units use half-wave rectifiers and 
others use a full-wave rectifier. In the first 
case, only half of the alternating voltage is 
used and when full-wave rectification is used 
both halves of the alternating voltage wave 
are utilized. The filter system may contain 
either one or two sections. Whether a half- or 
full-wave rectifier is used or whether a one- or 
two-section filter is used is something that need 
not particularly concern the prospective pur- 
chaser. The design of the filter in either case 
should be such as to eliminate any hum, and so 
long as the device which you buy does not hum 
excessively, you may be sure that the filter cir- 
cuit has been correctly designed for the type of 
rectifier used. The coils and condensers used in 
the filter circuit do not become weak with age, 
and a filter system capable of giving an output 
voltage free from hum will continue to do so 
unless some unit in the system completely fails. 



"high-low" switch in "high" position); 140 at 
20 mA., 120 at 30 mA., and 70 at 50 mA. (with 
"high-low" switch in "low" position). Other 
models supply about 10 volts less. Approval 
pending by National Board of Fire Underwriters. 
Raytheon rectifier is used. Two-section filter. 
Adjustable output voltages. Model A-i for oper- 
ation on 1 10 volts 50-60 cycles a.c.; Model A-}, 
25-40 cycles; Model A-4, 220 volts 50-60 cycles 
a.c.; Model A-8, 1 10 volts 50-60 cycles a.c. Size: 
Models A-i, A-3, A-4, 9x7x5} inches; Model 
A-8, 3x7x10 inches. Prices, including rectifier; 
Model A-i, $37.50; Model A-3, $42.50; Model 
A-4, $42.50; Model A-8, 27.50. 

BURNS, MODELS 75O-A, 750-6, AND 8oo-B 

Maximum output voltage of Models 75O-A 
and 750-6; 190 volts at 30 mA., and 180 volts 
at ;o mA. Model 8oo-B, 205 volts at 20 mA., 
and it)o volts at 30 mA. Uses Raytheon rectifier. 
Amplifier and detector voltages adjustable. 
Two-section filter. Approximately 20 watts a.c. 
input with 30 mA. load. Designed to operate 
171 type power tubes. Size: Models 75O-A and 
750-6; 7J x 10^ x 6f inches; Model 8oo-B, 
4! x io| x jf. Prices: Models 75O-A and 750-8, 
$47.50 with tube; Model 8oo-B, $35 with tube. 

AMRAD, MODEL No. 280 
Maximum output voltage; 200 at 20 mA., 180 
at 30 mA., and 165 at 50 mA. Uses type 280 




B POWER UNITS FOR YOUR RECEIVER 

.The power unit at the left is the Erla Steadivolt BC Converter and it utilizes a Raytheon BH rectifier tube and a glow tube to maintain the output 
constant at all loads. It v/ill supply up to 80 milliamperes at 180 volts. It lists at $40 including tubes. The Exide unit in the center and the Burns power 
device at the right both contain adjustable resistance units to regulate the voltage at the various terminals and further information regarding these 

two devices will be found in the listings on these pages 



using an electrolytic or tube rectifier is a matter 
of personal preference. 

WHEN YOU USE A B-POWER UNIT 

ALOUD hum audible in the output of a re- 
ceiver operated in conjunction with a B 
power unit may be due to coupling between the 
receiver and the power unit itself. If the hum is 
due to such a cause it can generally be eliminated 
by placing the power unit in some other position 
relative to the receiver. Also if hum is to be pre- 
vented it is essential that the negative B be 
grounded directly, and in some cases it is neces- 
sary to connect a i-mfd. 2Oo-volt condenser be- 
tween the grounded negative B terminal and one 
side of the input power lead. If these simple 
remedies do not eliminate the hum it is likely 
that there is some defect in the unit itself and 
the dealer should be consulted for, if the power 
unit is operating properly it should produce 
practically no audible hum in the output. Every 
plate-supply unit must contain a transformer 
designed to step up the input voltage to an 
amount depending upon what output voltage is 
required and upon what type of rectifying ele- 
ment is used. The rectifier, whether it be a tube 
or an electrolytic device, modifies the alternating 
current obtained from the power supply and 
changes it to a pulsating direct current. The filter 
circuit smooths out the pulsation in the rectified 



Facts About Some B Units 



ACME APPARATUS Co., MODELS E-i, E-2, -3, 
AND -4 

Maximum output voltage of a.c. models: 205 
at 20 mA., 185 at 30 mA., and 160 at 50 mA. 
Uses Raytheon BH rectifier. Two adjustable 
voltages. Two-section filter. Approved by Na- 
tional Board of Fire Underwriters. Size: 8J x 3} 
x 7f inches. Models E-i, -3, and -4 for opera- 
tion on 1 10 volts 60 cycles a.c. Model E-2 for 
operation on 120 or 220 volts d.c. Model E-i, 
with cable, for one- to twelve-tube sets, 850; 
Model E-2, with cable, for one- to twelve-tube 
sets, 25; Model -3, with cable, for one- to 
eight-tubes sets, $85; Model -4, with binding 
posts, for one- to eight-tube sets, $35. 

ACME ELEC. AND MFG. Co., MODEL BE-4O 

Maximum output voltage; 200 at 20 mA., 185 
at 30 mA., and 145 at 50 mA. Uses QRS rectifier. 
Two adjustable voltages. Full-wave rectifier. 
Two-section filter. Approved by National Board 
of Fire Underwriters. For operation on 1 10 volts 
50-60 cycles a.c. Recommended for five- to eight- 
tube sets with power tubes. Size: 7! x 1 1 J x 3|J 
inches. Price, with tube, $34.50. 

ALL-AMERICAN, MODELS A-i, A-3, A-4, AND A-8 

Maximum output voltage of Model A-8; 200 

at 2omA., 180 at 30 mA., 140 at 5omA. (with 



or 213 thermionic rectifier. One-section filter. 
Fixed output voltages. Full-wave rectifier. 
Twenty watts a.c. inpu, at 30 mA. load. For 
operation on 100-120 volts 60 cycles a.c. Size: 
ioi x 6J x 7j inches. Price, without tube, $45. 

ARCO B POWER 

Maximum output voltage: 180 volts at 50 mA. 
Uses filamentless rectifier. Two-section filter. 
Full-wave rectification. Fifteen watts input with 
30 mA. load. Size: gf x 3$ x 8| inches. For opera- 
ation on 1 10 volts 60 cycles a.c. Price, without 
tube, $32.50. 

BREMER-TULLY B POWER 

Maximum output voltage: 216 at 20 mA., 
195 at 30 mA., and 1 50 at 50 mA. Uses Raytheon 
BH rectifier. Output voltages adjustable by 
fixed steps. Two-section filter. Full-wave recti- 
fier. Seven watts input with 30 mA. load. Ap- 
proved by National Board of Fire Underwriters. 
Will supply receivers having up to ten tubes. 
For operation on 110-115 volts 60 cycles a.c. 
Size: 4j x gf x 6j inches. Price: $37.50, without 
tube. 

BASCO B POWER 

Maximum output voltage: 250 at 20 mA., 
230 at 30 mA., 190 at 50 mA., and 175 at 60 mA. 
Uses Raytheon BH rectifier. Two-section filter. 
Full-wave rectification. Fixed detector voltage. 
Other voltages variable. A special primary 
rheostat functions to regulate output to supply 
different types of power tubes. Twenty watts 



122 



RADIO BROADCAST 



DECEMBER, 1927 



input with 30 mA. load. Size: 12 x 45 x 7\ inches. 
Price, with tube, $35. 

KING, TYPES M AND V 

Maximum output voltage: 238 at 20 mA., 215 
at 30 mA., and 180 at 50 mA. Uses type 213 
rectifier. One-section filter. Full-wave rectifica- 
tion. Type M has variable detector and amplifier 
voltages. Type V has variable detector voltage 
and fixed 90, 135, and power tube taps. Twenty 
watts input with 30 mA. load. Can supply up to 
nine tubes. Size: Type V, 9! x 4^ x 7 inches; 
Type M, 1 1 x 6 x 6 inches. Prices: Type M, 
45.00; Type V, $37.50. 

EXIDE, MODEL 9-6 
Maximum output voltage: 208 at 20 mA., 




MAJESTIC, SUPER-B POWER UNIT 

Maximum output voltage: 186 at 20 mA., 
156 at 30 mA., and 112 at 50 mA. Adjustable 
output voltages. Special "high-low" switch 
gives two voltage ranges. Full-wave rectification. 
Two-section filter. For operation on 1 10 volts 
60 cycles a.c. Size: io| x 5! x 9 inches. Price, 
complete with tube, $29. 50. 

FRESHMAN, MODEL A 

Maximum output voltage: 220 volts at 40 mA. 
Uses tube rectifier in full-wave circuit. Adjusta- 
ble output voltages. Two-section filter. Unit 
supplies following C voltages: -45 -9, -40. 
Thirty watts input with 30 mA. load. Designed 
to supply sets using up to seven tubes. Price 
complete: $45. 

MUTER B POWER UNITS 

Two types made, one for Raytheon BH tube, 
the other for 2 1 3 or 280 type rectifier. Maximum 
output voltage (Raytheon type); 200 at 20 mA., 
1. 80 at 30 mA., and 150 at 50 mA. Other type 
gives output voltages about 10 volts lower. 
Full-wave rectification. Two-section filter. Fixed 
output voltages. Twenty-one watts input with 
30 mA. load. For operation on 110-120 volts 
60 cycles a.c. Prices: Raytheon model, $26.50; 
other model, $24. 50. 



30 mA. load. Adjustable detector voltage. 
Rheostat in the primary to compensate differ- 
ences in line voltage. Uses Raytheon type B or 
BH rectifier. Size: iij x 45 x 8j inches. Price: 
$34-50. 

DIS-TON, TYPES D-6o AND D-25 
Maximum output voltage: 215 at 20 mA., 
200 at 30 mA., and 185 at 50 mA. Adjustable 
output voltages. Two-section filter. Full-wave 
rectification. Fifteen watts input with 30 mA. 
load. Unit uses two thermionic rectifiers. Sup- 
plies C bias up to 22 volts. Self-contained milli- 
ammeter indicates performance. Price $29.50, 
without tubes. Type D-6o 

Maximum output voltage: 120 at 20 mA., and 
95 at 30 mA. Adjustable output voltage. One- 
section filter. Half-wave rectification. Nine watts 
input with 30 mA. load. Uses one thermionic 
rectifier. Size: 10 x 4 x 6 inches. Price: $23.50, 
with tube. Type D-25 




THREE MORE LINE SUPPLY DEVICES 



The Acme B power unit incorporating two variable resistances to compensate differences in load imposed on the device by different receivers is shown 

at the right. The All-American Constant B is illustrated at the center and contains a "high-low" switch to adapt the device to difierent loads and line 

voltages. The C potential as well as B potential can be obtained from the Valley unit at the left 



194 at 30 mA., and 180 at 40 mA. Uses electro- 
lytic rectifier, arranged in bridge circuit for full- 
wave rectification. Two intermediate and de- 
tector voltages adjustable. Two-section filter. 
For operation on 105-125 volts 50-60 cycles a.c. 
Ten watts input with 30 mA. load. Approved by 
National Board of Fire Underwriters. Designed 
to supply sets with six or more tubes. A 1 12 or 
171 type power tube may be used. Size, 6 x 
n| x 9! inches. Price: $42 50. 

GENERAL RADIO, TYPE 445 

Maximum output voltage: 200 at 20 mA., 
185 at 30 mA., and 160 at 50 mA. Uses type 280 
rectifier tube. Two-section filter. Output voltages 
adjusted by means of sliding taps on wire-wound 
resistance. C voltage available for power tube. 
Twenty-eight watts input with 30 mA. load. 
Designed to meet specifications of National 
Board of Fire Underwriters. Automatic switch 
breaks the i lo-volt a.c. input circuit when cover 
is removed. Size: 154X7x7 inches. Price: $55.00, 
without tubes. 

pREED-ElSEMANN, MODEL l6 

Maximum output voltage: 135 at 30 mA. 
Uses type 280 rectifier tube. Also uses type 874 
glow tube to maintain output voltages con- 
stant independent of the load. Two-section filter. 
Three C voltages available;-4j, -9, and -27. 
Twenty-five watts input with 30 mA. load. For 
operation on 105-120 volts 60 cycles a.c. Size: 
7x7x9! inches. Price: $35.00, without tubes. 



PRESTO-O-LITE "SPEEDWAY" B 
Maximum output voltage: 188 at 20 mA., 175 
at 30 mA., and 148 at 50 mA. Fixed output vol- 
tages. Compensation for variations in line volt- 
age obtained by adjusting three-point switch. 
One-section filter. Full-wave rectification. 
Twenty-five watts input with 30 mA. load. 
Uses Raytheon BH rectifier. Size: 6x8x8 inches. 
Price: $37.00, including tube. 

SENTINEL, MODEL B-C 

Maximum output voltage: 180 at 80 mA. 
Uses two rectifier tubes. Two variable voltages. 
Unit supplies two C voltages, -4! (fixed) and 
-45 to -45. Voltage control to compensate 
variations in line voltage. Beverly model is 
equipped with special instrument used to read 
the voltages being supplied by the various taps 
on the power unit. Prices, including two tubes, 
regular model, $44.50; Beverly model, $65.00. 

SILVER-MARSHALL, TYPE 656 

Maximum output voltage: 170 at 20 mA., 160 
at 30 mA., and 140 at 50 mA. Unit uses ux-213 
(cx-313) rectifier and ux-284 (cx-384) glow 
tube. Glow tube maintains output voltages 
practically constant independent of load. Two- 
section filter. Twenty-five watts input with 30 
mA. load. Size: 6j x 7^ x 5 inches. Price: $38.50. 

STEWART, U-8o 

Maximum output voltage: 190 at 20 mA., 175 
at 30 mA., and 140 at 50 mA. Two-section filter. 
Full-wave rectification. Thirty watts input with 



STERLING, TYPE R-97 

Maximum output voltage: 300 at 20 mA., 
286 at 30 mA., and 262 at 50 mA. Adjustable 
output voltages. Full-wave rectification. Twenty- 
five watts input with 30 mA. load. Unit supplies 
C voltages up to 50 volts. Price: $55.00 

VALLEY, MODEL 60 

Maximum output voltage: High range 250 
at 20 mA., 220 at 30 mA., and 175 at 50 mA.; 
Low range 200 at 20 mA., 180 at 30 mA., and 
140 at 50 mA. Uses Raytheon BH rectifier. Two 
adjustable voltages. Two-section filter. Full- 
wave rectification. Eighteen watts input with 
30 mA. load. Size: 5! x 9! x g\ inches. Price: 
$50.00, including tube. 

VALLEY, MODEL 40 

Maximum output voltage: 170 at 20 mA., 
145 at 30 mA., and 1 10 at 50 mA. Uses Raytheon 
BH rectifier. Two adjustable voltages. One-sec- 
tion filter. Full-wave rectification. Seventeen 
watts input with 30 mA. load. Size: 9 x 4j x -]\ 
inches. Price: $37.50, with tube. 

COMPO, MODEL B-C 

Maximum output voltage: 180 at 50 mA. 
Two-section filter. Full-wave rectification. Uses 
Raytheon BH rectifier. Uses Raytheon BR 
regulator tube to keep voltages constant. Unit 
supplies adjustable C voltages up to 50. Twenty- 
eight watts input with 30 mA. load. Size: loj 
x 5! x 8J inches. Price: $57.50, with tubes. 



Measuring the "GAIN of 



your RECEIVER 

*^ 






St 
/req 



romberg-Carlson engineers testing the audio-frequency characteristics of one of their No. 744 receivers. The apparatus consists of a "beat 
equency" oscillator which produces the audio tones, and meters for measuring the extent to which these frequencies are amplified within 



the receiver 



UR present broadcasting structure is 
made up of three intimately connected 
components, the broadcasting station, 
the receiving equipment, and the intervening 
medium. The broadcasting station has one 
raison d'etre to translate smjnd impulses into 
electrical waves; the receiver's only purpose is to 
accomplish the opposite to translate these 
electrical waves back into sound impulses. The 
intervening medium is the connecting link be- 
tween the transmitter and the receiver, an in- 
efficient link it is true, performing its task with 
many vagaries, and for reliability's sake it might 
be very well displaced by a metallic conductor. 
The radio medium, however, has the advantage 
that for broadcasting purposes, the communica- 
tion is radiated in all directions, and is not con- 
fined to a direct path between two points. 

We have already outlined in the November 
RADIO BROADCAST what the transmitter does 
when it lays down a "field strength" about the 
receiver, how this field strength is measured, how 
much is necessary for various degrees of service, 
and how field strength and the attributes of sets, 
selectivity, sensitivity, and fidelity, are related. 

It was pointed out that the greater the field 
strength, or the more sensitive the receiver, the 
more powerful the corresponding loud speaker 
signal. We are now faced with the problem of 
ascertaining how sensitive a receiver must be 
to deliver a certain signal from a certain field 
strength, how selective a set must be to shut out 
unwanted signals in favor of the desired program, 
and what the degree of fidelity must be to furnish 
sufficient realism to make a receiving equipment 
no longer a " radio" but a musical instrument. 

What we must do is to answer the following 
questions, presupposing a station to deliver a 
certain field strength at a certain point: 



By KEITH HENNEY 

Director of the Laboratory 



How loud will be the resulting signal from a 
certain receiver? How can it be measured? What 
will happen if another station a given number of 
kilocycles away goes on the air and lays down a 
certain field strength about the receiver? If the 
receiver is sufficiently sensitive and selective, 
how do these factors influence the fidelity? 




100 1M> 

MICROVOLTS INPUT 

FIG. I 

When one measures the output voltage of a re- 
ceiver of several years ago as the input voltage is 
changed, he gets a curve similar to those shown 
above. Note the steep i3OO-kc. curve indicating 
extreme sensitivity, and the decreasing sensitivity 
as the radio frequency is decreased 



Since radio receivers were first made, qualita- 
tive answers to these questions have been the 
stock in trade of all engineers. It is only within 
the last year that quantitative answers have been 
generally available, especially when one consid- 
ers the receiver as a single unit, and desires 
answers to his questions not with regard to the 
component parts that make up that receiver but 
with respect to the ensemble equipment. Meth- 
ods for determining the characteristics of coils, 
condensers, transformers, and other individual 
units that go to make up a "radio," have been 
known and used for several years. In England 
great emphasis has been laid upon and many 
arguments built around such measurements as 
contrasted with those which include everything 
in a receiver between antenna and loud speaker. 
While it is true that the characteristics of such 
units can be combined to produce a fair approxi- 
mation of what the complete receiver will do, an 
overall measurement carries much more convic- 
tion to the engineer. 

An interesting experiment was carried out at 
station WOR some time ago, and more recently 
by WLW, to enable listeners to determine how 
low and how high in audio frequencies their 
receivers were responsive. At WLW, where a 
Wurlitzer organ forms part of the studio equip- 
ment, continuous tones varying from the lowest 
to the highest organ note were put on the air, 
First the pure note of the open diapason was 
transmitted and then it was played with various 
harmonics added. This enabled the listener to 
determine not only the acoustic limits of his 
receiver and loud speaker but the change in 
quality as the harmonics modulated the original 
pure note. 

In laboratory the business of performing the 
same experiment or that of investigating the 



124 



RADIO BROADCAST 



DECEMBER, 1927 



sensitivity and selectivity of the receiver under 
better controlled conditions consists in moving 
the transmitter nearer the receiver, and decreas- 
ing its power accordingly. This eliminates the 
vagaries of the intervening medium, and when 
the transmitter is finally connected metallically 
to the receiver a set-up results which is suffi- 
ciently flexible that everything can be varied and 
measured at the same time. A miniature broad- 
casting station is necessary. This must consist 
of an r.f. oscillator whose output can be regulated 
and measured, an audio-frequency oscillator 
variable from the lowest to the highest audio 
tone ordinarily broadcast and relatively free 
from harmonics, and some means of combining 
these two generators of electric and sound waves. 

The Hazeltine Laboratories, under the direc- 
tion of Chief Engineer MacDonald, made such 
tests on receivers which were under development 
there, and the results were published in the 
Proceedings of the I. R. E. in February, 1927, the 
first paper to be published in this country on 
such laboratory practice. The emphasis here, 
however, was more on component parts, such as 
radio-frequency amplifiers, coupling coils, and 
audio amplifiers than on the receiver as a whole. 
The data as published were most interesting. 

In a discussion of this paper, appearing in the 
April, 1927, Proceedings of the I. R. E., H. D.Oak- 
ley and Norman Snyder of the General Electric 
Laboratories described the methods used several 
years ago at the Schenectady Laboratory for 
measuring receivers. 

The equipment was housed in two shielded 
rooms, one of which contained the radio and 
audio oscillators as well as a control device for 
regulating the voltage which was put on the 
receiver under test in the adjoining room. A 
standard Radiola 100 loud speaker was placed 
across the output of the receiver, and the voltage 
across it measured as the input voltage was 
varied. 

To test the sensitivity of the set, that is, to 
tell how many output volts could be delivered 
with a given input radio voltage, the following 
procedure was carried out. The generator was 
set going at a certain radio frequency and this 
was modulated at 1000 cycles to a given degree 
of modulation. The input to the receiver was 
varied in small steps until the output tube over- 
loaded. This was considered the upper working 
limit of the receiver. A specimen curve of out- 
put voltage plotted against input voltage is 
shown in Fig. i . The receiver was a standard set 
of several years ago, and is not indicative of the 
better types of modern sets. 

The data show that the receiver at 1300 kc. 
was roughly 6.5 times as sensitive as at 560 kc. 
and that to produce an output voltage of 16 at 
1300 kc. required an input of only 51 microvolts 
compared to 335 required at 560 kc. At 1000 kc. 
the voltage required was roughly 175. The out- 
put voltage at 560 kc. divided by the input volt- 
age gives a rough voltage gain of 46,000; at 1000 
kc. the ratio is 102,000 and at 1300 kc. the gain 
is 300,000. 

The data showed that the output voltage for 
each of the three frequencies was proportional 
to the input voltage squared, for which the de- 
tector tube is responsible. 

TESTING SELECTIVITY 

TO TEST the selectivity of the receiver, it 
was tuned to, say, 560 kc., and the output 
voltage read as the transmitting generator in 
the first of the two shielded rooms was varied in 
frequency but kept at constant amplitude. The 
receiver was then set at some other frequency 
and a similar set of data was taken. Specimen 
curves shown in Fig. 2, are taken from the 
Proceedings of the I. R. E. 




706050403020100102030405060TO 
KILOCYCLES OFF RESONANCE 

FIG. 2 

These queer curves show the selectivity of a 
rather poor receiver. At 560 kc. the set is se- 
lective, at 1300 kc., curve C, it is as broad as the 
proverbial barn door. They are indicative of a 
poorly engineered receiver and were made on 
sets sold several years ago 

The curves plotted from data obtained in this 
manner are given in Fig. 2, and show the field 
strength required to produce a given signal which 
differed from the frequency setting of the re- 
ceiver by a certain number of kilocycles. For ex- 
ample, if the receiver were accurately tuned to 
560 kilocycles, a signal 10 kilocycles off reson- 
ance, say 570 kc., required a field strength of 
150 microvolts per meter to produce an inter- 
fering signal. At 1300 kc., a signal 66 kc. away, or 
1366 kc., having a field strength of 150 micro- 
volts per meter, would produce the same inter- 
ference. 

In other words the receiver was roughly one 
seventh as selective at 1300 kc. as it was at 560 
kc. which, coupled with the fact that it was 
nearly seven times as sensitive at -the same 
frequency, may demonstrate why the higher 
broadcasting frequencies were not so highly 
regarded by engineers of transmitting stations 
a year or so ago. There is no reason why a care- 



fully designed and engineered receiver cannot 
be equally sensitive over the broadcasting band 
of 1000 kc. If the band were to be extended, in 
the direction of still higher frequencies, the 
problem placed upon design engineers would be 
considerable, but would not be insurmountable. 

Receivers of the present day are better than 
these curves show. Methods of maintaining equal 
gain over rather wide frequency bands are well 
known, and up-to-date receiver manufacturers 
make every effort to include in their products the 
results of all well-known inventions. A receivei 
which squawks at 1300 kc. and is practically 
silent at 560 kc. is a poorly designed set, and 
should not be placed in the same class as others 
in which care has been taken to avoid just such 
criticism. 

The method of measuring and rating receivers 
employed by the Radio Corporation of America 
was described in The Proceedings of the I. R. E. 
in May, 1927, by T. A. Smith and George Rodwin 
An arbitrary loud speaker signal is set up and 
all measurements are made with a view toward 
determining the field strength required to pro- 
duce this signal, which is that corresponding tc 
an average audio-frequency (r.m.s.) voltage ol 
1 5 across a 5Ooo-ohm resistance when a 4OO-cycle 
note modulates the transmitter to a degree ol 
50 per cent. 

Having determined how much output voltage 
the receiver will deliver when a certain input 
voltage due to a certain field strength is im- 
pressed on it, mathematics will tell how much 
voltage or power will be delivered at other inpul 
levels, up to the overloading point of the ampli- 
fier tubes. The following relations express the 
manner in which transmitter antenna power, 
input receiver voltage, output voltage and powei 
are interconnected: 

Field strength a transmitter antenna current. 
Field strength a square root of transmitter power 
Input receiver voltage a field strength. 
Output receiver voltage oc field strength squared. 
Output receiver voltage a. transmitter power. 
Output receiver power a output voltage 

squared. 
Output receiver power a input voltage to the 

fourth power. 




FIG. 3 

The receiver is put through its paces in this shielded room at the General Electric Company 

Only signals that are meant for the receiver arrive at its input via shielded wires; all others are 

excluded by the shielding surrounding the six room surfaces 



DECEMBER, 1927 



MEASURING THE "GAIN" OF YOUR RECEIVER 



125 



Output receiver power a field strength to the 

fourth power. 
Output receiver power a transmitter power 

squared. 

The Greek letter alpha in the above relations 
means "is proportional to." 

Doubling the transmitter antenna current 
multiplies the transmitted power by four, dou- 
bles the field strength, doubles the input receiver 
voltage, multiplies the receiver output voltage 
by four, and multiplies the power into the loud 
speaker by sixteen. These relations may be con- 
nected to what happens in one's receiver by the 
following facts. The average stage of audio am- 
plification has a voltage gain of twenty-five, a 
two-stage affair having a voltage gain of roughly 
| 300, or 50 TU, if a 171 type tube is used as the 
1 output tube. A good radio-frequency amplifier 
! should have a voltage gain of about 50 TU, or 
i 300, so that the overall gain in voltage from a 
\ modern well engineered receiver should be in the 
[ neighborhood of 100,000, or 100 TU. These 
i figures in power amplification become respec- 
j lively, for the two-stage amplifier and for the 
omplete receiver, 30,000 and 10,000,000 truly 
mormous amplification. 

In actual practice the R. C. A. engineers do 

not measure the voltage across the resistance in 

he output of the receiver while the input voltage 

s varied. An interesting short cut is used in- 

tead, which is possible from the phenomenon 

accompanying the function of detection. 

When the receiver is tuned to a carrier wave, 
modulated or not, the average d.c. detector 
current changes, increasing when a C bias de- 
ector is employed, decreasing when the con- 
ventional grid leak and condenser method is 
used. Greater changes occur with greater field 
itrengths. or the more nearly the receiver is 
:uned to the incoming signals. The change in 
detector plate current, then, is a measure of the 
effectiveness of the field strength or the sensitiv- 
ty of the receiver. 

To produce the arbitrary 15-volt signal across 
:he 5ooo-ohm resistance in the receiver output 
requires a certain change in detector plate cur- 
rent. Once this is determined the audio amplifier 
can be dispensed with and all measurements may 
>e made by noting the change in detector plate 
current. This method obviates the necessity of 
using modulated signals. 

In the R. C. A. Laboratory the input voltages 




FIG. 4 

Signal generating apparatus used at the General Electric Laboratories for testing the characteristics 
of receivers. This apparatus is housed in a shielded room, and consists of a Heising modulated gen- 
erator capable of oscillating at any frequency in the present broadcasting band modulated at any 
audio frequency between 40 and 10,000 cycles 



are fed to the receiver through a dummy antenna 
consisting of an inductance of 28 microhenries 
which has a resistance of 2 ohms, a capacity of 
0.0004 mfd., and a resistance of 23 ohms. The 
curves obtained in this way show the same 
general characteristics as those given in the 
General Electric report, i. e., low gain at low 
radio frequencies, high gain and poor selectivity 
at high frequencies. At the same time there is 
considerable loss of the higher audio frequencies 
at the longer wavelengths, due to the excessive 
sharpness of tuning, or selectivity. 

While it is true that only a few of the larger 



and better-known receivers are engineered with 
these thoughts and these laboratory measure- 
ments in mind, it is a fact that more and more 
radio manufacturers are becoming aware that 
good engineering is a priceless asset. The article 
in this issue of RADIO BROADCAST on the Fada 
receivers, by John F. Rider, and others to follow 
on other well-designed receivers, proves this 
statement. The Laboratory is preparing data on 
manufactured sets using the methods of measure- 
ments mentioned above and as fast as the ma- 
terial is ready, it will be presented to RADIO 
BROADCAST'S readers. 



All About Patents 

INVENTIONS AND PATENTS, THEIR DEVELOPMENT 
AND PROMOTION. By Milton Wright, LL.B. 
Published by the McGraw-Hill Book Com- 
pany, Incorporated, New York. Price, $2.00. 
Pages, 225. 

A VERY useful contribution to the bewild- 
ered inventor, throbbing with the thrill 
of a discovery, is the sage and practical 
counsel of Mr. Milton Wright, as embodied in 
tlis new book, "Inventions and Patents." There 
is nothing assuming about the writer's style; 
the work is not overburdened with technical legal 
arguments, although the subject is a highly 
technical one, and there is no obscure language 
to confuse the uninitiated. 

The subject matter of the volume is devoted 
broadly to all the problems which face the in- 
ventor. He is told what is patentable and what is 
not patentable, what constitutes a practical in- 



vention, what steps to take to facilitate securing a 
patent and how to protect it after it is secured, 
how to select a good patent attorney, how a pat- 
ent should be applied for, how to obtain financial 
support, what the problems of marketing and 
merchandising are, how to sell patents outright, 
on a territorial and on a royalty basis, and what 
steps to take against infringers. There you have 
it in one long sentence; certainly the scope of the 
book is broad enough to be a real aid to the 
floundering inventor. 

Valuable cautions and dangerous pitfalls, 
which are the usual stumbling blocks to the un- 
initiated patent seeker and inventor, are dis- 
closed. For example, how to keep records which 
aid in establishing date of conception and re- 
duction to practice, is explained so that the in- 
ventor, heeding the advice given, will have no 
difficulty in later sustaining his invention in the 
courts. And again, the vital subject of how to se- 
lect a patent lawyer and how to get the greatest 
value from his services is presented simply and 



clearly. The book abounds in practical illustra- 
tions which serve to clarify the force of the wri- 
ter's arguments. 

The reviewer does not hesitate to recommend 
a thorough reading of this volume to all those 
who believe they have a patentable idea and 
those who contemplate obtaining a patent. It is 
certain either to cause them to abandon the idea 
because it offers little or no possibility for profit, 
or else to secure a better and more easily pro- 
tected patent. Considering that only one patent 
out of a hundred secured by hopeful inventors 
proves profitable, the discouragement of the 
impractical is as valuable a service as the en- 
couragement of the promising. In this respect, 
Mr. Wright's dispassionate and constructive 
point of view differs materially from the flam- 
boyant literature and booklets which un- 
scrupulous patent lawyers distribute in the hop2 
of inveigling misguided inventors to obtain 
patents, whether their ideas show promise or not. 

E. H. F. 





A LOUD SPEAKER ELEMENT 

This is the driving unit used in the type 20-20 cone speaker 
manufactured by A. H. Grebe. The speaker is priced at $35.00 



A PACENT OFFERING 

This well made instrument uses a balanced armature con- 
struction that insures quality reproduction. Price, $35.00 





THE "ALGONQUIN" CONE 

SPEAKER 

An artistically designed cone priced at 
$15.00, the product of the Algonquin Elec- 
tric Company 



A POWER CONE WITH B SUPPLY 
The perfectly free mounting used in this Mag- 
navox combination is responsible for its excel- 
lent reproducing qualities. It contains a 210 
power-amplifier and B supply. Price, $242.00 






THE "NEUTROWOND" REPRODUCER 
An attractive loud speaker finished 
in American walnut. Price $35.00 



AN INNOVATION 
This interesting loud speaker made 
by Frank B. Porter, Washington 
utilizes the structure above the base 
to conceal a tonal chamber. The ac- 
tual element is with base. Various 
models retail for from $50.00 to 
$150.00 

126 



FADA 

This 17-inch table cone sells for $25.00, Model 

315 A. Fada manufactures other more expensive 

models selling for up to $50.00 





FOUR OR SIX-VOLT A-POWER 

A combination storage battery and full-wave dry rectifier available in 

four and six-volt models, made by Triple A Specialty Co., Chicago. 

Price: either model. $39.50 



THE BASCO A-B POWER UNIT 

This device contains a B-Power unit anil n storage battery-trickle char- 
ger combination. A visual indicator shows the state of charge of the 
battery. Price $75. 




A TWO AMPERE "TUNGAR" BATTERY 

CHARGER 

A well known product of the General Electric 
Company for charging A and B storage batteries. 

Price, $18.00 



THE "ACME" B POWER UNIT 



For use with receivers containing up to twelve 

tubes, including a 171 type power tube. A Ray- 

theun rectifier is used. Price: $50.00 





ANOTHER B POWER UNIT 

This unit supplies up to 135 volts at a 60 milliam- 
pere load mc-rc than enough for most receivers. Man- 
ufactured by the All- American Company and priced 

at $27.50 



A POWER AMPLIFIER AND B SUPPLY 

An A-B-C power supply for receivers using a.c. tubes. The uniteon- 
tains one stage of power amplification using a 210 tube. Manufac- 
tured by the Radio Receptor Co., New York, and priced at $60.00 



127 



FACTS ABOUT THE FADA "SPECIAL" SET 

By John F. Rider 




JUST as the research laboratory is the prime 
mover of every business, whether cheese, steel, 
or clothing, it is also the heart of the radio in- 
dustry. The radio public is awakening to the 
fact that research is a prime mover in the radio 
industry; that research, and research only, can 
produce faithful reproduction, ample volume, 
satisfactory selectivity, ease of control, and per- 
fect stability. The result is recognition of re- 
search as the paramount factor, and consistent 
with this recognition, is the gradual stabiliza- 
tion of the industry its gradual ascension to 
an impregnable position. 

Research is directly responsible for every 
good receiver and for every development in ra- 
dio receiver design since the day KDKA com- 
menced its broadcasting activities. A good radio 
receiver cannot be produced without a research 
background. 

As an example, let us consider a typical re- 
ceiver, the design of which may be laid directly 
at the door of research. This receiver consists 
of three stages of radio-frequency amplification, 
a non-regenerative detector and two stages of 
audio-frequency amplification. It is known as 
the Fada "Special." But before we can enter 
into the mechanics of the receiver, we must first 
ascertain why the electrical design used was se- 
lected. 

The problem placed before the engineering 
department was the development of a radio re- 
ceiver limited to six tubes. The apportioning of 
the tubes was the first problem. How many 
stages of radio-frequency amplification should 
there be; and how many stages of audio-fre- 
quency amplification? Having developed audio- 
frequency transformers with known response 
characteristics and known gain per stage, and 
knowing that a two-stage audio amplifying 
system using their transformers would give the 
proper amount of amplification, the engineering 
department decided upon two stages of trans- 
former-coupled audio amplification. Since the 
detector unit utilizes but one tube, the remain- 
ing three tubes can be applied to the radio- 
frequency system. 

The development of the radio-frequency sys- 
tem brings to light many interesting features. 
Should the stages be tuned or untuned or a com- 
bination of both? Should the stages be shielded, 



and what material shall be used for the shield- 
ing? Since the receiver utilizes an antenna as 
the pick-up system, the three stages of radio- 
frequency amplification will give a high degree 
of sensitivity. The demand for selectivity neces- 
sitates the use of tuned stages of radio-frequency 
amplification. But the development of a three- 
stage tuned radio-frequency amplifier does not 
mean a simple decision to use three stages. Con- 
sideration must be accorded to the wavelength 
response of such a system. The average system 
possesses wavelength characteristics which fall 
in amplification as the wavelength is increased 
i.e., the amplifying power of the radio-frequency 
amplifier is high at the shorter wavelengths and 
as the tuning dials are manipulated to tune to 
the longer wavelengths, the amplification de- 
creases, and at 550 meters is a fraction of that 
at 250 or 300. meters. This situation must be 
avoided; it is desirable that the receiver should 
possess equal amplification over the entire broad- 
cast frequency spectrum. 

Since the allocation of frequencies to broad- 
casting stations is such that excellent selectivity 
can be obtained with two stages of well-designed 
and shielded tuned radio-frequency amplifica- 
tion, the third stage can be utilized to balance 
the two tuned stages and give the system the 
desired wavelength response characteristic. The 
radio-frequency system would, therefore, con- 
sist of two stages of tuned radio-frequency am- 
plification and one stage of untuned radio- 
frequency amplification. 

The decision to shield the individual stages 
was immediate, since shielding, if properly car- 
ried out, is conducive to better radio receiver 
operation and consequently better radio recep- 
tion and better stability is thus attained in the 
radio-frequency stages because coil interaction 
is eliminated. By the elimination of coil inter- 
action, neutralization is made more effective. 
Better tone quality is also obtained, because by 
eliminating coil interaction, the side-band char- 
acteristics planned in the design of the tuned 
stages are actually obtained. Selectivity is aug- 
mented, because direct coil pick-up is precluded. 
The elimination of coil pick-up also means 
greater amplification in the radio-frequency 
system. 

The selection of the shielding material is 



governed by the effect the shield has upon the 
inductances used in each stage. In order to mini- 
mize the electrical effect upon the coils, a ma- 
terial with a high conductivity must be used, 
since high conductivity means lower losses. 
Aluminum was decided upon, and the shield 
takes the form of a can, completely enclosing 
the radio-frequency transformer. With the 
shields of proper diameter and properly located 
with respect to the coils, the losses introduced 
are so small as to be entirely negligible. 

In view of the fact that the radio-frequency 
coils are shielded, it is possible to make use ol 
the most efficient type of winding the single- 
layer solenoid. Without shields, a cascade sys- 
tem employing such coils would be quite diffi- 
cult to control. The selection of the single-layei 
solenoid was also based upon the fact that il 
can be wound with the greatest degree of ac- 
curacy, particularly so when the winding fern- 
is grooved, and the turns ar; wound in thes< 
grooves. 

The receiver is to be dual tuned, requiring 
two condensers controlled by one drum dia 
and another single condenser controlled by th< 
other drum dial. Such control is simple becausf 
of the precision methods employed in the test- 
ing and matching of the coils and tuning conden- 
sers. Each tuned transformer consists of three 
windings, the primary, the secondary, and 2 
neutralizing winding. Each of these winding; 
is matched on a radio-frequency testing instra 
ment, to within one eighth of one per cent. Th< 
coil under test is plugged into an oscillator cir 
cuit and a resonance point obtained with a Stan 
dard condenser. This condenser is so graduates 
that a 10 per cent, variation in resonance ii 
spread out across the loo-division dial. The dia 
settings for the resonance point for each winding 
are noted and the coils segregated according tc 
these figures. The result is that each group o 
three coils consists of coils with windings whicl 
never vary more than one eighth of one per cent 

The same precision in testing applies to thi 
tuning condensers, and because of the mechani- 
cal design of these condensers, full accuracy ii 
maintained during the operating life of tht 
unit. Each completed tuning condenser is mad< 
to within one per cent, plus or minus, of its ratec 
capacity, and each condenser in a group of threi 
is matched to within one eighth of one per cent 
of the others. The matching of the variable con 
densers is carried out by means of a specia 
radio-frequency measuring instrument designe< 
for the purpose. 

The construction of variable condenser: 
which will not vary more than one per cent, call: 
for detailed engineering. The brass used for thi 
plates must be very accurate, the toleranci 
limit being 0.0005 f a m '' ' n thickness. To as 
sure perfect alignment of the condenser plates 
and a smooth rotary action, large bearings an 
used, these latter being approximately |" ii 
diameter. To further assure perfect alignment o 
the brass plates, each plate is individual!; 
stipled and leveled. 

But the precision construction and matchinj 
of coils and condensers is not sufficient to assun 
perfect operation. It is necessary to assure per 
feet mechanical support for these units sup 
ports which will be identical in every receiver o 
similar design. It is necessary to select a base fo: 
the condensers which will assure easy operation 
not for a short while, but for years to come 



DECEMBER, 1927 



FACTS ABOUT THE FADA "SPECIAL" SET 



129 



Again engineering comes to the fore, with a pressed steel chassis J" 
thick, punched out on a loo-ton press. One operation punches all the 
holes necessary and also forms the chassis. The result is uniformity of 
mounting holes. 

R. F. CHARACTERISTICS 

WITH the condensers, coils, and shields on hand, we go back to the 
radio-frequency system. The overall gain curve of the three-stage 
radio-frequency amplifier, consisting of the two tuned stages and the one 
untuned stage, is shown in Fig. i. Here we see a beautiful example of re- 
search and engineering. With the exception of the zone between 200 and 
212 meters, (1500 and 1410 kc.) the amplification does not vary more 
than ii per cent, from 212 to 550 meters. Between 200 and 212 meters, 
the curve rises with the increase in wavelength, and the difference be- 
tween the lowest point, 200 meters, and the highest, 250 and 500 meters, 
is only 17 per cent. With such small variance in amplifying power, the 
owner can manipulate the dials of his receiver from 200 to 550 meters, 
and know that the sensitivity of the system is practically uniform over 
the complete scale. 

But the design of a radio-frequency system does not consist solely of 
the development of an amplifier which will possess the wavelength re- 
sponse curve shown. It is also imperative to accord detailed consider- 
ation to the shape of the resonance curve of each individual tuned stage, 
since the resonance curve manifests a great influence upon the tone qual- 
ity of the receiver. In this respect, there is a close association between 
the radio-frequency amplifier and the audio-frequency system. Many 
owners of radio receivers are unaware of the effect the resonance curve 
of the radio frequency stages has upon the tone quality obtainable with 
the receiver employing three stages of radio-frequency amplification. 
Fans are too prone to overlook the side-band characteristics of the radio- 
frequency stage. They forget that while the radio-frequency stage is 
tuned to the frequency of the carrier wave, it is also necessary to con- 
sider that this carrier wave is modulated by audio frequencies rang- 
ing from 30 to 5000 cycles. Also that the effect of these modulating fre- 
quencies is to create a modulated carrier wave whose frequency spec- 
trum is 10,000 cycles wide. In other words, if the carrier wave (un- 
modulated) is 750,000 cycles (400 meters) when modulated, this wave 
is broadened to cover from 745,000 to 755,000 cycles. The 5000 cycles 
above the carrier and the 5Ooo-cycle-band below the carrier constitutes 
che side-bands. Hence the resonance curve of the radio-frequency stage 
must be broad enough to cover this band of 10,000 cycles even though 
the circuit is actually tuned to 750,000 cycles. If the curve is too sharp, 
some of the higher side-band frequencies will be suppressed. If the 
curve is too broad, selectivity will be marred. Hence both selectivity 
and sideband suppression must be considered in the design of the radio 
frequency amplifier. With a known value of "Q", which is the factor of 
selectivity, being the ratio of the reactance to the resistance of the cir- 
cuit at a certain frequency, it is imperative to know the side-band sup- 
pression in the radio-frequency amplifier and to give it consideration 
in the design of the associated audio-frequency amplifying equipment. 
An example of various degrees of sideband suppression in tuned circuits is 



-Neutralizing Condensers --_. 
' 



Antenna 



60 



= 40 

i-: 

z 

z 
320 



\ r 

R.F. GAIN 



^00 250 300 350 400 
WAVELENGTH, METERS 

FIG. I 



450 



500 550 



The curve shows the gain from the antenna to the input to the detector. 
The sensitivity of the r. f. amplifier is high and the amplification flat 



110 



Width of carrier.& side bands 




in o ir> 

rH Oil CM 



Lower side band *"" ~"^ Upper side band 

MODULATION FREQUENCIES 

FIG. 2 

Tuned circuits that are too selective impair quality. The outer curve shows 
the response in a well-designed circuit 



UX-171 




FIG. 3 

This is the complete circuit diagram of the Fada "Special" receiver. 

The '.'amplification equalizer" shown above, consisting of an untuned 

stage, especially responsive to the longer wavelengths accounts for the 

excellent r. f. response curve in Fig. I 



-CPower-C4!$ 



rr 

*C -A + A -BjgB45 tB90*BPower 
BATTERY CABLE 



130 



RADIO BROADCAST 



DECEMBER, 1927 



50 



40 



20 



10 



A.F. CHARACTERISTIC 



V 



100 



FREQUENCY 
CYCLES PER SECONO 



1000 



10,000 



FIG. 4, OVERALL A. F. CHARACTERISTICS 



shown in Fig. 2. Curve A shows 80 per cent, 
suppression on 5000 cycles and curve B shows 
15 per cent, suppression at 5000 cycles. Curve 
B is broader than A, but the proper amount of 
selectivity is obtained by virtue of the cumula- 
tive effect of a number of stages. 

THE DETECTOR 

FROM the radio-frequency system we pass 
on to the detector circuit. A choice of two 
systems of detection is available the grid bias 
method or the grid leak-condenser arrangement. 
Because of the increased sensitivity, resulting 
in greater output, the grid leak-condenser sys- 
tem is used. 

From the detector we pass to the audio- 
frequency amplifying system. We made mention 
in a previous paragraph that transformers were 
used, but the design of a transformer-coupled 
audio amplifier cannot be. consummated by 
simply deciding upon transformers. Sometimes 
these characteristics of the transformers to be 
used are exactly what the requirements call for; 
sometimes they are not. With specific require- 
ments on hand, audio-frequency transformers 
must be designed to fill the need. The design is 
a detailed process. First the tubes to be used 
must be decided upon, and their electrical con- 
stants must be taken into consideration. The 
core material for the transformers must be 
selected, and the inductance of the primary and 
secondary windings must be calculated in order 
that the transformer possess certain predeter- 
mined characteristics. The method of winding 
must be decided upon so that distributed capac- 
ity is low and so that satisfactory response on 
the higher audio frequencies is obtained. 

Detailed consideration must be accorded to 
the regeneration existing in the completed audio- 
frequency amplifier. This is very important. 
The overall response curve of a two-stage audio 
system with regeneration in the amplifier will 
differ from that of a single unit. If the single 
unit is designed to match the radio-frequency 
system, the operation of the completed two-stage 
amplifier will be entirely different. It is also 
essential to consider the loud speaker to be used. 
This unit, too, possesses operating character- 
istics which must be taken into account. The 
combined operating characteristics of the radio- 
frequency amplifying system and the audio- 
frequency amplifying system must be such 
as to produce best results with a particular loud 
speaker or with a group of good loud speakers. 

The completed two-stage audio amplifier of 
the receiver under consideration the Fada 
"Special" possesses the overall audio frequency 
characteristics shown in Fig. 4. The amplifica- 
tion is shown on the ordinate or the left vertical 
line. The audio frequencies are shown on the 
abscissa or the horizontal line. The frequencies 



are plotted on a logarithmic scale. As is evident, 
the curve is practically flat from 50 to 1000 
cycles, rises from 1000 to 3000 cycles, and' then 
falls gradually to 5000 cycles. The maximum 
difference in amplification between the lowest 
and the highest points is only 12.5 per cent., 
which difference is negligible, since the average 
ear will not discern intensity variations of such 
small proportions. 

The development of the receiver is com- 
pleted. Let us now consider the engineering in- 
volved in the testing of the receiver. Each re- 
ceiver must undergo various tests during the 
process of production. The designing of this 
testing equipment is also in the hands of the 
engineering staff. Without testing equipment 
all the effort placed in the design of the indi- 
vidual parts and systems will have been for 
naught. Without a testing department the life 
of a radio plant would be very short. 

The first test is a continuity test of the as- 
sembled chassis. This makes necessary testing 
with meters in each and every circuit, showing 
the voltage across the tube filament, the fila- 
ment current, the plate current, the plate volt- 
age and, continuity in the grid circuit. The fila- 
ment current and filament-voltage meters show 
the operating action of the units incorporated in 
these circuits. The same is true of the plate- 
voltage and plate-current meters. Open circuits 
in the plate circuit will be shown on these me- 



ters. By simultaneously testing all the circuits, 
it is easy to select the faulty circuit if one is 
present in the receiver. The location of the fault 
is also noted. By having meters in every circuit 
it is unnecessary to hunt haphazardly. 

The second test is to determine the efficacy 
of the neutralizing system, and the adjustment 
of the neutralizing units. In this test the as- 
sembled and wired chassis is connected to a 
series of meters, and the input system is coupled 
to a dummy antenna which obtains its energy 
from a local radio-frequency oscillator. The 
dummy antenna simulates an average outdoor 
installation. The meters show excessive regen- 
eration in any of the tuned circuits, when these 
circuits are made resonant to the frequency of 
the oscillator. The neutralizing system is then 
adjusted until all signs of excessive regeneration 
in the radio-frequency amplifying system dis- 
appears. Incidentally, this same method of test- 
ing is employed to determine the overall gain 
of the radio-frequency amplifier. 

When measuring the amplifying power of the 
radio-frequency system, from the grid of the 
first radio-frequency amplifying tube to the grid 
of the detector tube, a constant predetermined 
radio-frequency signal is fed into the radio- 
frequency system. The input voltage is held 
constant on all wavelengths covered by the 
tuning system. The voltage across the grid fila- 
ment circuit of the detector tube is measured 
with a vacuum-tube voltmeter. 

The third test applied to the receiver is the 
"air" test, i.e., the receiver is connected to an 
outdoor antenna and outside broadcasting sta- 
tions are tuned-in. This test is a final check of 
all the tests applied to the receiver during the 
process of manufacture. The overall gain of the 
radio-frequency amplifier and the audio-fre- 
quency amplifier is again ascertained. With 
respect to the measurements of the audio-fre- 
quency system and the transformers used, each 
transformer is individually tested against a 
standard before being placed into service in the 
amplifier. Then the completed two-stage unit 
is again tested under actual operating condi- 
tions. With a known constant input, the total 
gain is finally measured with a tube voltmeter 
the last of a series of thorough and efficacious 
tests. 




WHAT THE CHASSIS LOOKS LIKE 



i 6 



Our Readers Suggest " 



TWO pages of RADIO BROADCAST will regularly 
be devoted to publishing contributions from 
readers who have made interesting improvements 
in the use of ready-made radio products. These 
suggestions may deal with complete radio receivers, 
socket-power units, "kinks" in the placing of loud 
speakers, or slight circuit or mechanical changes 
in apparatus in general use. Our readers have a 
wealth of experience along these lines and these 
pages offer an opportunity for them to share their 
findings. Typewritten contributions from readers 
are welcomed which, if published, will he paid for 
at our regular space rates. In addition, a monthly 
award of $ I o will be paid for the best contribution 
published each month. Address all contributions to 
Complete Set Editor, RADIO BROADCAST, Garden 
City, New York. THE EDITOR. 



A Short-Wave Converter for any 
Radio Receiver 

THERE is to-day sufficient material being 
broadcast below 100 meters (3000 kc.) to 
interest the serious fan and to justify the 
construction of simple apparatus for its reception. 
In some cases the use of a short-wave receiver 
will make possible the reception of important 
programs beyond the range of the conventional 
receiver. The construction of a short-wave re- 
ceiver is often an expensive proposition, and con- 
verters heretofore described have been rather 
complicated affairs. It is the intention of the 
writer to describe a simple and inexpensive con- 
verter which, when attached instantly to any 
broadcasting receiver, makes it possible to re- 
ceive on wavelengths between 15 and 125 meters 
(20,000 and 2400 kc.) No change is made in the 
present receiver but by means of the converter 
the former is alternately available for short- or 
broadcast-wave reception. 




THE SHORT-WAVE CONVERTER 

The short-wave converter takes the form of a 
very simple and incidentally highly efficient 
short-wave receiver, the output of which is 
connected to the audio-frequency amplifier of the 
present broadcast receiver. A simple plug-in 
arrangement makes the change a matter of a few 
seconds. 



The following is a list of the parts used in the 
short-wave converter illustrated and described: 

Li, L 2 , U Set Aero Short-Wave Coils. 

Ci Amsco o.ooo25-Mfd. S. F. L. Condenser. 

Lc Silver-Marshall Choke. No. 275 

Ri Clarostat o-joo.ooo-Ohm Resistor. 

RZ Amsco 3-Megohm "Grid Gate-/' with 

Mounting. 

Rs Amsco 2O-Ohm Rheostat. 
C 2 Tobe o.ooo25-Mfd. Fixed Condenser. 
Cs Tobe o.ooi-Mfd. Fixed Condenser. 
Three Four-Foot Lengths of Flexible Wire. 
Sub-Panel Brackets, Hardware, and Old Tube 

Base. 

National Type C Dial. 
Amsco Floating Socket. 
7 x 12 x T " s Inch Celeron Panel, 
yxiixj Inch Wood Baseboard. 
Two "XL" Laboratories "Push" Binding Posts. 




THE FRONT PANEL 

The construction of the short-wave converter 
is best described in the accompanying illus- 
trations. However, a word regarding the con- 
necting plug may be of assistance. 

The three wires leading respectively from the 
radio-frequency choke coil, A-battery minus, and 
A-battery plus, are led to the base of a discarded 
tube, as made clear by reference to Fig. i. The 
glass of the old vacuum tube is broken off and 
the base cleaned out. The three wires are soldered 
to terminals inside the base, one to the A-plus 
plug, one to the A-minus plug, and one to the 
plate terminal. These terminals may be identified 
by holding the tube base, bottom down and the 
side pin toward you. With the base in this 
position, the two rear posts are A plus and A 
minus respectively from left to right, and the 



left-hand front post is the plate terminal. The 
base of the tube is now filled with a wax com- 
pound, such as the top of a discarded B battery. 
This is easily done by placing small pieces of the 
wax in the tube base and melting them with a 
hot soldering iron. The receiver may be wired 
with bus bar, but the author found coded flexible 
wire more convenient. All leads should be made 
as short as possible. 

The function of the choke coil is important. 
If the Silver-Marshall one is not available, one 
may be made by winding 100 turns of 26 d.c.c. 
wire at random on a wood spool, 5 inch in 
diameter with j-inch wooden core. 

To operate the short-wave converter, remove 
the detector tube from the regular broadcast 
receiving set and place it in the tube socket of 
the converter. Next select the plug-in coil from 
the Aero set covering the wave band in which 
you wish to receive, and plug it into the coil 
jacks. Then insert in the detector tube socket 
of the regular broadcast receiver the plug made 
from the old tube base. When the antenna 
and ground have been changed to their respective 
posts on the converter, you are ready to listen-in. 
To do so simply leave the loud speaker where it 
is, or, if phones are used, these may be plugged 
in as usual in any stage for which a jack is pro- 
vided on your particular receiving set. Turn the 
Clarostat until the receiver oscillates. Tune-in a 
station and clear up the signal by a further ad- 
justment of the Clarostat or rheostat as re- 
quired. 

PERRY S. GRAFFAM. 
Boston, Massachusetts. 

STAFF COMMENT 

\A/HILE the importance of short-wave 
" * reception cannot be overstressed, state- 
ments regarding its immediate and direct utility 
to the fan must be qualified. RADIO BROADCAST 
does not care to encourage the use of radiating 
short-wave receivers, and the more simple sets 
necessarily fall into this category. Serious experi- 
menters, broadcast enthusiasts desiring to take 
up code work, and fans in isolated districts are, 
however, undoubtedly justified in conducting 
experiments along these lines. Mr. Graffam's 
inexpensive arrangement offers perhaps the sim- 
plest introduction into the realm of megacycles. 



R.F. Choke 

^MKKTi 

1-4 



FIG. 1 




132 

Short-wave reception is by no means an un- 
alloyed bliss as some avid publicity men would 
have us believe. Ninety-eight per cent, of the 
transmissions carried on below 100 meters is 
inter-communicative code work and the two per 
cent, of radio telephonic transmission is often 
marred by high speed fading. 

Antenna Compensation in a Single- 
Control Receiver 

NE of the major problems in single- 
control multi-tuned circuit receivers is 
the elimination of the detuning effect 
of the antenna on the first radio frequency 
stage. Loose and variable coupling between the 
antenna primary and the first r.f. secondary is 
generally employed to compensate this influence. 
These arrangements, unfortunately, often lower 
the signal response of the receiver, and the set 
still functions best with antennas of definite 
electrical characteristics. 

The arrangement proposed overcomes these 
difficulties and offers the following advantages: 

It eliminates the antenna effect on any receiver. 

It can be attached to any receiver without 
making more than one simple change. 

No additional controls are required. 

Sensitivity is never reduced. On the contrary 
it is often increased. 

Any length antenna may be used with the 
receiver without making additional changes. 

The device acts as a partial blocking stage in 
case oscillations are set up in the tuned amplifiers. 

In brief, the device causes the radio-frequency 
impulses to be applied across a resistor to an 
extra radio-frequency tube, which is outputted 
to the original antenna primary. 

The following is a complete list of parts neces- 
sary to make the change: 

Ci o.oo I -Mfd. Coupling Condenser. LI R. F. 
Choke Coil. Socket. 2O1-A Type Tube. Ri J- 
Ampere Ballast Resistor. Sw. Battery Switch. 
R 2 lOOO-Ohm Resistor. Six Binding Posts. 

This apparatus is easily wired on a baseboard 
in accordance with the diagram, Fig. 2. 

The antenna is disconnected from the receiver 
and wired to post number one. The ground re- 
mains connected to the receiver and is also wired 
to post number two of the new stage. 

Turn on the filaments to the receiver proper 
and the switch to the extra stage. Run a wire 
from the A battery plus post on the set to post 
number four. The extra tube will probably light. 
If it does not light, repeat the test with a wire 
from the negative A post. 

If the extra tube lights with one side grounded 
and the other side connected to the A battery 
circuit, it is an indication that one side of the A 
circuit is grounded, as it will be in 90 per cent, 
of receivers. If this is the case, proceed as follows: 

Leave the wire that lights the filament con- 
nected to post number four. Connect the an- 
tenna post on the receiver to post number five. 

If, upon making the tests with the filament 
wires to post number four, the tube does not 
light, indicating that the filament circuit is 
not grounded in the receiver, the filament plus 
wire should be connected to post four and the 
filament minus wire to post three. The tube will 
now light, of course.. Connect the antenna post 
on the receiver to post number five, and terminal 
six to the plus 90 volts, and the unit is ready for 
operation. 

There is no change in the operation of the 
receiver whatever. If taps are provided on the 
antenna primary of the original receiver, slightly 
higher efficiency may be secured by experiment- 
ing with them. 

If the experimenter is a bit more of an expert, 



RADIO BROADCAST 

1 II I 


u 

1000 D 

2 


( 


Jiallast C 
<ReJ.istor < 

I"' 

swTl 

i>3 A4 m 


S 0.001 mfd 
3 R.F. Choke 

D6 


< 




FIG. 2 

the filament lead, or leads, to the antenna 
coupler tube may be led from the tube side of the 
set switch, making it possible to operate the 
antenna coupling tube by the same switch that 
controls the set filaments. 

HAROLD BOYD. 
Winchester, Virginia. 



AN EMERG-' 
ENCY AN- 
TENNA 

Fifty turns of 
bell wire are 
usually satis- 
factory 



STAFF COMMENT 

THE arrangement suggested by Mr. Boyd is 
quite practicable and is already used in 
several commercial and kit receivers. The tube 
coupling device is in the nature of an untuned 
radio-frequency amplifying stage, and, in some 
instances, may result in increased sensitivity. 
The r.f. gain, however, is generally small in 
comparison with the utility of the arrangement. 
One thousand ohms is about the optimum 
value for the antenna coupling resistor. It seems 
to make little difference whether the resistor is 
inductive or not. The Lynch, Amsco " Metaloid," 
Carter, and Electrad are excellent resistors for 
this purpose. A variable zero to 2000 ohm re- 
sistor may be substituted for the fixed resistor 
recommended by Mr. Boyd and used as a vol- 
ume control. 

In a few cases it may be found that the load 
imposed by the coupling arrangement on the 
first r.f. transformer is no more favorable to 
tandem tuning than that of the average antenna. 
This can be compensated either by adjusting the 
compensating condenser across the first tuning 
section (if the main condenser is so equipped), 
or by winding a special primary over the first 
secondary. From six to ten turns of wire may be 
placed directly over the coil. One end is con- 
nected to post number five in Fig. 2 and the other 
terminal to plus 90 volts. 

Increasing Response from a Loop 
Receiver 

AL receivers are more or less affected by 
location, but the loop set seems to be 
particularly susceptible to adverse con- 
ditions imposed by position. This is due to the 
fact that the loop is often surrounded by steel 
building framework and similar obstructions 
which the open antenna can rise above. Dis- 
advantages of this nature were impressed upon 
the writer when moving from the top floor of a 
New York City apartment house to the second 
floor of the same building. The receiver, a 



DECEMBER, 1927 

Radiola super-heterodyne, worked perfectly in 
its original position eight floors higher up, but 
lost perhaps seventy-five per cent, in sensitivity 
when brought a hundred feet nearer the ground. 

Its operation was brought up to normal by a 
simple device, thrown together in five minutes. 
A twenty-five foot antenna was strung on the 
roof of the building. Three turns of wire, harmon- 
izing with the wire on the loop, were wound 
around the loop frame, twisting slightly about 
the original loop wire to keep it in place. One end 
of this extra wire was connected to the short 
antenna, while the other end ran to ground. 

Sufficient energy is transferred to the loop 
circuit from the open antenna to compensate the 
losses imposed by an inferior location. 

A. J. HOWE. 
New York City. 

STAFF COMMENT 

THE device recommended by our contributor 
is, of course, a simple antenna coupler, the 
extra turns of wire functioning as the primary 
and the loop itself as the secondary. The arrange- 
ment is effective. On the ordinary super-hetero- 
dyne (that is other than the second harmonic 
type) the shortest antenna giving satisfactory 
reception should be used, to reduce the possi- 
bility of radiation. 

The directional effect of the loop is largely 
eliminated by coupling to an open antenna in 
this manner. However, the selectivity of the 
super-heterodyne is such that this effect can be 
safely dispensed with. 

A coupling device of this type is made com- 
mercially by the Jenkins Radio Company, 
Davenport, Iowa. 

A Temporary Antenna for the 
Traveling Fan 

EXTRA tubes and batteries are easily avail- 
able in an emergency, but the occasion 
where a spare antenna would save the day 
is seldom provided for, so a word as to an ex- 
cellent makeshift antenna may not be amiss. 
A first class one, often equal to the average 
outdoor variety, may be secured by wrapping 
fifty turns of bell wire around a telephone desk 
stand. See Fig. 3. One end of the wire is con- 
nected to the antenna post on the receiver and 
the usual ground is used. 

The writer, an inveterate radio enthusiast, 
discovered the possibilities of this arrangement 
when traveling across the country with a Fada 
neutrodyne, the operation of the receiver being 
somewhat limited by the facilities of the average 
hotel bedroom. 

Subsequent experiments show this type of 
antenna to be equally efficacious with other 
receivers. 

ALFRED A. MARKSON. 
New York City. 

STAFF COMMENT 

THE use of the telephone as a substitute 
antenna is by no means a novelty, although 
the exact system of connection outlined here is 
not that generally advocated, but probably as 
efficient. The more widely used application of 
this idea is found in the use of a small metal 
plate upon which the telephone is stood, and 
which is connected to the antenna binding post 
of the receiver. Such metal plates, especially cut 
for the purpose, are commercially available. As 
the latter are not always immediately obtain- 
able in an emergency, Mr. Markson's idea is a 
useful one. 




A radio set of other years can be brought up to date by improving the audio quality through 
new transformers, tubes and loud speakers or by the purchase of a complete power-supply- 
amplifier unit. These changes help greatly. R.f. Changes are not suggested 



THE articles appearing in the September 
and October issues of RADIO BROADCAST, 
dealing with the judging and attainment 
of good tone quality, resulted in hundreds of 
letters from readers, asking specifically how cer- 
tain makes of receivers could be converted to 
give the high-grade tone quality described. It 
was the writer's intention to answer the letters 
directly in these columns, but their number grew 
so large that it would require an entire issue of 
the magazine to meet the demand for informa- 
tion. This article is based upon the questions 
raised in the letters and will serve as a concen- 
rated answer to these letters. 

Hundreds of thousands of radio enthusiasts 
are owners of receiving sets sufficiently selective 
:o be satisfactory, but falling far short of the 
atest standards of tonal reproduction. So long 
as the receiver meets the simple requirement of 
>eing sufficiently selective, but not too selective, 
t can be converted to give good tone quality. 
The writer does not mean to imply that the 
radio-frequency end of the modern receiver is 
not as greatly improved as the audio end and 
that the most satisfactory measure, after all, is 
not to discard entirely the obsolete receiver. 
But not everyone is in a position to employ 
this remedy; some of us must reconcile ourselves 
to tuning with several dials and to great sensi- 
tiveness at the high frequencies, where it is not 
especially needed, and lack of sensitiveness at 
the low-frequency end, where it is most desired. 
Simplicity of control, and equal amplification 
throughout the wavelength scale, are features 
embodied only in the latest receivers. But, given 
satisfactory selectivity, an old receiver may be 
greatly improved so far as tone quality is con- 
cerned. 

Exceedingly sharp tuning, such that high- 
power stations within fifty ot a hundred miles 
are heard with considerable volume only when 
tuned-in precisely and always disappear with a 
whizz and hiss when detuned but one or two de- 
grees from exact resonance, indicates selectivity 
too great for the attainment of good tone qual- 
ity. Oftentimes a receiver behaving in this way 
can be made to tune more broadly, so that 
neither the low or high audio frequencies are cut 
off, by installing a somewhat longer antenna. 

Having once determined that the radio- 
frequency end of the receiver does not tune too 



By EDGAR H. FELIX 

sharply, improvement of tonal quality is a mat- 
ter of re-vamping the audio system. The essen- 
tial requirements for good tonal quality are: 
(i) Audio-frequency transformers of sufficiently 
good quality to pass the entire tonal range; (2) 
tubes of sufficient power and emission to ade- 
quately handle signals of considerable magni- 
tude (3) a power supply assuring correct A, B, 
and C voltages to every tube under actual oper- 
ating conditions; and (4) a loud speaker capable 
of setting up sound waves throughout the audio 
scale. 

Prior to recent developments in transformer 
design and material, resistance-, and impedance- 
coupled amplification were the only systems, 
within reach of the experimenter, capable of 
handling broad tonal Jange. These systems under 
proper conditions are not excelled in quality 
output by high-grade modern transformers, but 
require an extra stage so that they are not 
easily incorporated in a manufactured receiver, 
unless it is especially designed to accommodate 
them. During the last year, transformer devel- 
opment has reached such a point that two 
stages may be used to give the best of tone qual- 
ity. 

Transformers can be manufactured at a cost 
as low as forty cents, although the actual raw 
materials which go into the better transformers 
cost as much as eight times that figure. Expen- 
sive iron alloys, which magnetize and de- 
magnetize rapidly, and high-inductance wind- 
ings, are essential if the entire tonal range is to 
be amplified. Under no circumstances, can cheap 
transformers serve as well as well known expen- 
sive ones. In replacing transformers, to make the 
job worth while, confine yourself to the best. 
Some of the better receiving sets of earlier vin- 
tages, are not equipped with suitable transform- 
ers and the substitution of such makes as Amer- 
tran, Ferranti, Silver Marshall, Thordarson, 
General Radio, Rauland Lyric, Modern, All 
American, Pacent, Sangamo, and Samson, to 
mention some of the better ones, is decidedly 
worth while. 

REPLACING OLD TRANSFORMERS 

TO DETERMINE whether such substitu- 
tion is feasible, open the cabinet and ex- 
amine the audio-frequency transformers. See if 
they are easily removed and if the four terminals 



are so marked that you can put labels on the 
wires before you remove them, indicating the 
correct filament, grid, plate, and B -(-terminals. 
This will prevent confusion when you put the 
new transformers in place. Adhesive tape is a 
convenient form of label. Measure the space 
available for transformers because cheap trans- 
formers are often small. The high grade ones, 
with which you replace them, are likely to be 
somewhat larger and hence may not fit in the 
space provided for the old transformers. Where 
the problem requires moving of sockets and 
other parts, your local dealer can replace the 
transformers for you. His charge should be be- 
tween two to five dollars, plus the cost of the 
transformers themselves. 

The next link in the chain of audio reproduc- 
tion concerns the tubes used. You cannot hope 
to secure good quality, if you do not use a power 
tube in the last stage. The ux-2oi-A (CX-JOI-A) 
tubes in the output stage are capable of only 
moderate volume with good quality. If you are 
attaining fair quality with such tubes now, after 
replacement of the transformers they may prove 
unsatisfactory, because the added energy in the 
low frequencies, impressed upon the output 
tube by the new transformers, will not be handled 
satisfactorily. 

In the case of the storage-battery receiver, 
wired with but a single C battery connection, 
both the first and second stages are usually sup- 
plied with the same C battery voltage, generally 
4J. Re-wiring of the set, however, is not neces- 
sary to put in an ux-iyi (cx-3yi) or a ux-i 12 
or cx-312. Manufacturers such as Na-Ald, have 
developed special sockets with flexible cable con- 
nections, enabling you to add the necessary grid 
and plate voltages to operate power tubes, with- 
out any wiring changes. 

There is one exception to the general rule that 
replacement of the transformers and addition of 
a power tube will bring you better tone quality. 
Certain reflex receivers, which enjoyed a fairly 
wide sale three and four years ago, are not 
adapted to this simple conversion. The use of a 
grid bias and plate potential satisfactory for 
audio purposes may render the radio-frequency 
amplifier of these reflex sets quite unstable. 
Many of these receivers are such heavy con- 
sumers of plate current that discarding them is 
an economy. It is not worth while to attempt to 



134 



RADIO BROADCAST 



DECEMBER, 1927 



improve them. You must treat them as you 
would an inherited 1902 one cylinder-automo- 
bile. 

With dry-cell tube receivers, the largest out- 
put tube available is the 120 type. This is a great 
improvement in power handling capacity over 
the 199 type, but it is still far from sufficient to 
attain really good tonal quality. The further 
down the tonal range the reproducing system 
goes and that is what gives body and richness 
to music and naturalness to speech the greater 
must be the power available in the output tube. 

The owner of such a dry-cell tube receiver 
need not, however, abandon hope, because he 
may employ a one-stage power amplifier, receiv- 
ing its filament, grid and plate potentials, di- 
rectly from the light socket, and employing the 
ux-2io (cx-jio) in the output. This tube is of 
even greater power handling capacity than the 
ux-iyi (cx-37i) and, hence, capable of magni- 
ficent tonal quality, provided good transform- 
ers and reproducers are used in connection with 
them. These light socket units may also be 
used with storage battery outfits and are recom- 
mended to B battery users. The use of a power 
tube in the output stage considerably increases 
B battery drain and, as a consequence, the use of 
a light socket amplifier unit is an economy. 

Such power supply devices are manufactured 
by General Radio, Farrand, Radio Receptor. 
Pacent, National, Timmons, Amertran, and the 
Radio Corporation. They furnish A, B, and C 
power, not only for the 210 or 171 tube, but also 
B and in some cases C voltages for the receiv- 
ing set itself. Adding these amplifier-power 
supply devices to the existing receiver is a simple 
matter. The tonal reproduction secured is still 
dependent upon the grade of loud speaker and 
first stage transformer used but, so far as avail- 
able power is concerned, the purchase of a good 
power amplifier and B supply unit settles that 
question. 

SELECTING A REPRODUCER 

HAVING now supplied transformers which 
actually amplify the entire range of tonal 
frequencies, having installed tubes of adequate 
power handling capacity, and having supplied 
them with the correct A, B, and C voltages, it is 
next necessary to obtain a loud speaker capable 
of setting up sound waves throughout the entire 
tonal range. A loud speaker which is seemingly 
satisfactory with poor transformers and power 
supply, often fails when the high-grade trans- 
formers and tubes are wired into circuit, because 
of the larger load and greater frequency range 
thereby impressed upon it. 

Remedying an audio system requires that the 
entire audio system be put in good condition, 
because any one weak link will destroy the ef- 
fectiveness of all the other remedial measures. 
If you have four worn out tires on your car, 
replacing one, two, or three of them is not suf- 
ficient to give you immunity from tire trouble. 
Many a person, dissatisfied with tone quality, 
has replaced his loud speaker and then wondered 
why great improvement did not result. In fact, 
it often happens that an exceptionally good loud 
speaker will sound worse than a bad one with a 
poor set. The good loud speaker sets up sound 
waves in exact accordance with the electric 
signal furnished it. A poor loud speaker may be 
so designed as to exaggerate the low notes, thus 
providing for their deficiency in a defective au- 



dio system. When a good loud speaker is sub- 
stituted, the absence of low notes, due to un- 
suitable transformers, becomes more conspicu- 
ously apparent. 

Every reproducer has an actuating element 
which sets up the sound waves a sort of paddle 
which sets up air vibrations. With good repro- 
ducing systems, the loud speaker must be ca- 
pable of setting up low frequencies as well as 
high ones, and consequently the actuating ele- 
ment, vibrating diaphragm, or cone surface, must 
often be large if it is to be successful. The horn, if 
one is used, must also be of large size, so that it 
does not impede the radiation of low frequencies. 
A long, goose-necked horn chokes off the low 
frequencies, while a large exponential horn can 
give you much of the true magnificence of the 
organ. 

The writer cannot attempt to list entirely 
all good cones and horns, but he has personally 
tested Western Electric, Farrand Sr., Balsa, 
Rola, and Amplion, and found them capable of 
handling the output of 171 and 210 type tubes 
throughout the tonal range attainable by the best 
of amplifier systems. 

Inferior loud speakers fail not only because 
they are incapable of mechanically setting up 
waves by reason of small moving surface or con- 
fined tubular horn areas, but also because the 
electromagnetic unit is incapable of handling 
the large output which is necessary to secure 
good tone. With the 210 and 171 types of tubes, 
an output transformer or choke and condenser 
feed to the loud speaker is absolutely necessary 
to eliminate the direct-current component from 
the speaker winding. We desire only to have the 
audio-frequency fluctuations in the loud speaker 
winding so that magnetic saturation is avoided. 
Silver-Marshall, General Radio, Federal, Na- 
tional, Pacent, Samson, Thordarson, Amertran, 
Muter, Amsco, and others make output devices. 

One question which appeared in many of the 
letters received was the demand for more vol- 
ume, or specific questions to the same effect, 
such as whether the use of a 171 tube would 
increase volume. None of the measures described 
have for their purpose the increasing of volume 
output of the receiver. The use of large power 
tubes simply increases the amount of signal vol- 
ume which can be handled without distortion 
due to overloading. 

By using the grade of transformers, tubes, and 
loud speakers mentioned, a signal so weak that 
it can hardly be distinguished by the phones in 
the detector output circuit is amplified to com- 
fortable living room volume. If the signal is not 
sufficiently strong to give such volume, the 
remedy does not lie in additional audio-frequency 
amplification but in the use of a more sensitive 
receiving set. The best results are obtained if 
the detector tube's output is a signal just strong 
enough to be discernible in the headphones. 
Those complaining of weak signals should look 
to improving antennas and to increasing radio- 
frequency amplification. The audio system 
should not be expected to make up for deficien- 
cies in the radio-frequency amplifier. 

As a matter of fact, most of the receiving sets, 
even those of two and three years ago, are ade- 
quately sensitive. Many complaints of reduced 
volume may be attributed to the continued use 
of depreciated power supply and tubes, whose 
filaments have lost their emission. 

It is an essential requirement of good tone that 



the power supply be adequate and that the 
tubes have plenty of emission. There is only 
one way that this can be determined definitely 
and that is by measurement. Your dealer should 
have a tube checker which he can bring to your 
set, or you should take the tubes to a well 
equipped radio store for testing. By taking out 
one tube, substituting for it a plug, connected 
by a flexible cord to the set checker or tube tester, 
and placing the removed tube in a socket pro- 
vided on the tester, the A, B, and C potentials, 
and the plate-current output of the tube, can 
be measured. The writer recently tested an elab- 
orate set checker made by a concern in Detroit, 
equipped not only to make the four measure- 
ments mentioned, but also the voltage at the 
terminals of the A battery, the completeness of 
all the circuits and, the mutual conductance of 
the tubes by the manipulation of a few well 
marked switches. Every dealer should have 
some such device. The use of a voltmeter does 
not tell the full story and no dealer is in a posi- 
tion to service adequately without measuring 
devices such as those made by Jewel, Weston, 
General Radio, Quick-Test, Hoyt, Hickok and 
others. 

There were many well-known and widely ad- 
vertised makes of receivers which last year 
became known for their mediocre tone quality 
and which this season have effected extraordin- 
ary improvements. The importance of tone 
quality has been widely recognized and manu- 
facturers have realized that they cannot remain 
in the radio market unless their receivers are 
capable of high-grade reproduction. Name, rep- 
utation, price, and the willingness to submit 
their product to the test and approval of the 
recognized set expert, are guides to the set pur- 
chaser. Many receivers, described in most al- 
luring terms in general magazines, do not meet 
the laboratory inspection of the expert. It is best 
to confine your purchases to sets recommended 
by well-informed enthusiasts who have some 
familiarity with the technical phases of radio. 
In the October issue, the writer gave suggestions 
for tests which may be made at the dealer's 
store when a receiver is being demonstrated, 
to give indication of its tonal capacity. It is sug- 
gested that the reader go over both the Sep- 
tember and October articles before making pur- 
chases. 

To summarize, the conversion of an old re- 
ceiving set to give good tonal quality requires: 

(i). That the radio-frequency amplifier of 
the receiver does not tune so sharply that near- 
by signals are heard only when precisely in re- 
sonance. 

(2). Audio-frequency transformers be used of 
a quality and price sufficient to assure that they 
will amplify the entire range of frequencies 
from stage to stage. 

(3). The output tube be of sufficient power 
capacity to handle the required range ampli- 
tudes. 

(4). The correct A, B, and C voltages be sup- 
plied to the tubes. 

(5). That the loud speaker be capable of 
handling the tonal range. 

In most cases, these objectives are attained by 
replacement of the audio-frequency transform- 
ers, installation of a power tube (in the case of 
dry-cell sets, the addition of a one-stage power 
amplifier and B supply which furnishes A, B, 
and C power for a 210 or 171 type tube), and 
finally, the use of a suitable reproducer. 



A Quality Five-Tube A. C Receiver 

^^' / 



By JAMES MILLEN 




T^ 
_ 



I HIS article describes the construction of 
an a.c. operated receiver, the new type a.c. 
tubes being used to accomplish the electri- 
fication. In the preceding article in this series, 
published in last month's RADIO BROADCAST, 
some general information on a.c. tubes was 
given. 

In explaining how to use these a.c. tubes with 
an actual receiver, we have chosen a circuit which 
embodies some of the features of the Browning- 
Drake receiver. Strict adherence to the instruc- 
tions contained in this article will result in a light 
socket operated receiver equaling in sensitivity 
and selectivity a receiver operated on standard 
storage-battery type tubes. 

Before going into details regarding the con- 
struction of this a.c. receiver, we will point out 
how the circuit differs from that of Browning- 
Drake sets. First, let us consider the r.f. ampli- 
fier. Most previous designs of the Browning- 
Drake receiver have used a 199 type tube as the 
r.f. amplifier, because the tendency for this tube 
to oscillate is less than with a aoi-A type tube. 
A. c. tubes, however, have characteristics similar 
to the latter type, and since an a.c. tube is used 



FRONT VIEW OF THE RECEIVER 

in the r.f. stage of the receiver described here, it 
becomes necessary to devise some practical 
method of preventing this r.f. amplifier from 
oscillating. 

In Fig. 4 is shown, at "A," the circuit of the 
original Browning-Drake radio-frequency ampli- 
fier using Hazeltine neutralization; at "B" we 
see the Browning-Drake circuit using the Rice 
system of neutralization. At "C" is shown the 
circuit arrangement for use of a 226 type a.c. 
tube. In the grid circuit will be noticed a non- 
inductive resistor, having an ohmic value of 
approximately 1000 ohms. It is the use of this 
grid resistor or, as it is more generally called, 
"suppressor," that makes possible the balancing 
of the circuit. As this resistor is not placed in the 
tuned circuit, it has no detrimental effect upon 
the selectivity of the receiver. 

The arrangement shown at "C," Fig. 4, is 
used in the final model of the receiver illustrated 
in this article, and it will be noted that the plate 
voltage is fed to the plate of the tube through a 
choke coil, U, instead of through the primary 
winding of the r.f. transformer. The former 
method (feeding the voltage through a choke 



coil) tends to somewhat stabilize the operation 
of the receiver, especially when a socket-power 
unit is used for the B supply. 

The antenna is coupled to the first coil in the 
usual manner, i.e., through a 50-150 micro- 
microfarad midget variable condenser, to a 
center tap on the coil. If the antenna is over 40 
feet in length, the connections should be as indi- 
cated in the diagram, but if a shorter antenna is 
used, the lead from the midget condenser may 
connect directly to the grid end of the coil in- 
stead of the center. In congested localities, ex- 
cellent reception, with greatly improved selec- 
tivity, is obtained by using a j-foot length of 
bus bar for an antenna. The bus bar should be 
attached directly to the grid end of the coil. 

THE AUDIO AMPLIFIER 

THE audio channel employed is capable of 
producing excellent tone quality and at the 
same time lending itself equally well for use with 
either the new a.c. tubes or the standard storage 
battery tubes. The wiring of the audio channel 
is shown in the complete circuit diagram. Fig. 2. 
In the first stage is employed an impedance 



6 b 6 b 

2.5 1.5 

A.C. Filament 




Heating Transformer 



To Light 
Socket 



FIG. I 

Complete circuit diagram of the complete a.c. operated receiver 



136 



RADIO BROADCAST 



DECEMBER, 192-; 



IWi- 



T" 



T 



"75 

i "t^ 



c-1 



.~~"t 

r- 1 **-- 



NOTE: Holes with No.28 Drill 
unless otheiwisenolei 



FRONT PANEL 

FIG. 2 
How to drill the front panel 



coupling unit which is incorporated a radio- 
frequency choke coil; in the second stage, resist- 
ance coupling is used, while the third stage em- 
ploys a special arrangement of resistance and 
impedance with the impedance in the grid circuit 
of the power tube so as to eliminate any tendency 
of the amplifier to " motor-boat " when used with 
some types of B power units. A tone filter, Ls, is 
incorporated in the output circuit as a protective 
device for the loud speaker. 

As will be noted from thecircuitdiagram, Fig. I 
resistance-capacity filters (Rs-Cy, Rz-Ce, and 
R 8 -C 8 ) are employed in the grid circuits of each 
of the audio tubes. These filter circuits prevent 
"motor-boating" and make the operation of the 
audio amplifier entirely stable under all con- 
ditions. The grid bias resistances, Ra and RS, as 
well as the mid-tapped resistance, R 2 , across the 
filament of the detector tube, are all of the fixed 
variety so as to eliminate needless adjustment 
and enable the home constructor to obtain the 
same excellent performance from his receiver as 
from the original laboratory model. 

The various photographs, working drawings, 
and circuit diagrams accompanying this article 
give all the necessary details regarding the con- 
struction of this receiver and only a few ad- 



C7 C3 



C2 



C6 C10 C9 




R4 R 2 

FROM THE UNDER SIDE 

The letters correspond with the parts list on page 137. On page 33 of RADIO BROADCAST for 
November, 1927, appeared a back panel view of this set to which reference may be made 




-- 20 '^ . 

BASE PANEL 

FIG. 3 
How to drill the base panel 



Make Two, Brass 



+tfr 



*<w - 

* 


E 


tS 


^' 


> 

r 


1%1-^ 
i 1 




BRACKET 



DECEMBER, 1927 



A QUALITY FIVE-TUBE A. C. RECEIVER 




FIG. 4 

' The circuit of "C" is used in this set. This 
alteration in the usual Browning-Drake circuit is 
necessary because of the special problems arising 
from the use of a.c. tubes 

ditional hints need be given in order to make 
possible the easy construction of the receiver. ' 

As the illustrations show, the a.c. filament 
heating transformer is not built into the set, it 
being more convenient in this case to mount it 
as a separate unit within the usual battery com- 
partment of the console if the latter is employed. 

The first construction step is to drill the front 
and sub-panels in accordance with the details 
given in Figs. 2 and 3. 

The next step is to mount the condensers, 
coils, sockets, and other parts on the sub-panel, 
as shown in the illustrations. Then, the sub-panel 
may be almost completely wired all before 
attaching the front panel, which merely carries 
the dial, volume control resistor, and tickler 
adjustment. 

The small General Radio neutralizing con- 
denser should be disassembled and built right 
into the sub-panel after discarding the triangular 
bakelite back. 

In the receiver shown in the illustrations, the 
resistor mountings and sockets were also dis- 
assembled and the contacts remounted directly 
on the sub-panel. Much needless work can be 
saved however by retaining the bases of the 
resistor mountings and sockets. 

Instead of numerous binding posts the use of 
two cables is recommended. One cable should 
consist of the seven low-voltage a.c. leads to 
the filament transformer while the other cable 
should have four leads to the B power supply 
unit. 



As the loud speaker cord may be plugged 
directly into the tip jacks on the front of the 
tone filter, it is necessary to provide but two 
binding posts for the antenna and ground. 

The wire to use for all connections as well as 
the cables should preferably be No: 18 tinned 
flexible rubber-covered wire. Such wire may be 
obtained from Acme and Corwin in different 
colors for making the cable and to facilitate the 
tracing of the set wiring itself. 

With many uy-22y type detector tubes it will 
be found that the most satisfactory operation is 
obtained when the heater voltage is slightly be- 
low the rated 2.5 volts. For this reason it is 
recommended that a 6-inch length of resistance 
wire from an old 6-ohm rheostat be connected in 
series with one of the a.j-volt a.c. leads, prefer- 
ably right at the transformer terminal panel. 

ADJUSTING AND OPERATING THE RECEIVER 

THE adjustments necessary in order to obtain 
the best performance from the~completed 
receiver are few and easily made. First, connect 
the antenna, ground, loud speaker, B-power 
unit, and filament heating transformer, and then 
turn on the i lo-volt supply and wait for about a 
minute or so for the detector tube to reach its 
proper operating temperature. If a high-resist- 
ance voltmeter is available, the next step is to 
set the detector B voltage to approximately 45 
and the r.f. B voltage to 70. Should a suitable 
voltmeter not be available, the r.f. and detector 
B voltage may be set by guess work and then 
readjusted for best results later. The next step 
is to set the potentiometer, Ri, for minimum 
hum. Generally this adjustment will be obtained 
when the contact arm is somewhere near the 
center of its arc. Occasionally, if the receiver 
should develop a slight hum, a slight readjust- 
ment of the potentiometer will remedy the 
trouble. 

The antenna series condenser should be ad- 
justed so that the two tuning condenser scales 
read somewhat alike. 

The neutralizing condenser may now be ad- 
justed so that the receiver does not oscillate at 
the shortest wavelength when the tickler coil is 
set for minimum regeneration. Generally the 
proper setting is with the movable plate of the 
neutralizing condenser turned in about a third 
of the way. 

When making any of these adjustments, the 
volume control should be set for maximum vol- 
ume in which position the receiver has the 
greatest tendency to oscillate. The following is a 
list of parts recommended for use in the receiver 
described in this article: 



LIST OF PARTS 



TI National B-DiE Tuning Unit 

(Without Dial) 

T 2 National B-D2E Tuning Unit 

(Without Dial) 

National Drum Tuning Control . 
Li National Impedaformer, 1st Stage 

Type 

La National Impedaformer, 3rd Stage 

Type 

L 3 National Tone Filter .... 
Ra General Radio No. 439 Center-Tap 

Resistor 

Rs Lynch 5OO-ohm Suppressor 

Ci Precise No. 940 Midget Condenser, 

50-150 Mmfd 

Cs General Radio Midget Neutraliz- 
ing Condenser 

Re, R?, Rs Lynch o. i-Meg. Standard 
Metalized-Filament Resistors . 
Rg Lynch o.i-Meg. Type C Metal- 
ized-Filament Resistors . 
Rio Lynch o.5-Meg. Standard Metal- 
ized-Filament Resistors . 
Rn Lynch looo-ohm "Suppressor" . 
Rs Lynch 2ooo-Ohm Type P Wire 

Wound Resistor 

Ri Lynch 2-Meg. Standard Metal- 
ized-Filament Resistor . 
Cs, Q, C?, Cs, Cio Tobe i-Mfd. By- 
pass Condensers 

Cg Tobeo.i-Mfd. Bypass Condenser. 
Ria Electrad Royalty Variable Re- 
sistor, Type K 

C4 Sangamo o.ooo25-Mfd. Mica Con- 
denser .... ... 

Cs Sangamo o.ooi-Mfd. Mica Con- 
denser 

U Samson No. 85 R. F. Choke . 
R 4 Carter 2o-Ohm Midget Potentio- 
meter 

Two Eby Binding Posts .... 
Four General Radio No. 439 ux 

Sockets 

One General Radio No. 438 UY Sockets 

Eight Lynch Single Resistor Mountings 

Bakelite Panel, 7x21 Inches . 

Bakelite Sub-Panel, 9 x 20 Inches. 

Wire, Etc . 



137 



$ 8.25 

11.75 
6.00 

5.50 

5 50 
6. 50 

.60 
i.if 

i 75 
1.25 
2.25 
i .00 

50 

75 

1.25 
50 

4.50 
.60 



TOTAL 



ACCESSORIES 

One cx-371 (ux-i7i) or Ceco j-yi 
Tube 

One cv-327 (uY-227) or Ceco R-27 
Tube 

Three cx-326 (uv-226) or Ceco R-26 
Tubes 

One ux-28o (cx~38o) 

One National No. F226 Filament Heat- 
ing Transformer 

One B-Power Unit, National Type M . 
TOTAL 



$4.50 
6.00 

9.00 
5.00 

10.00 
40.00 

$74.50 



Looking Back 

THE STORY OF RADIO. By Orrin E. Dunlap, 
Jr. Published by the Dial Press, New York. 
Price $2.50; pages, 226; illustrations, 15. 

THIS book, by the Radio Editor of the 
New York Times, is a literary effort to 
squeeze some more thrills out of radio 
for the benefit of laymen who desire knowledge 
but do not want to struggle for it. There is 
nothing technical in its two hundred or so pages 
but, in a journalistic and often very interesting 
fashion, it gives a history of radio progress, and 
manages to touch on such topics as transmission 
theories, fading, radio direction finders, and 
piezo-electric control. The various branches of 
radio communication, such as aircraft work and 
transatlantic radio telephone circuits, are des- 
cribed; there are several pages on auditory 
phenomena; short waves and television are not 
neglected. The history of radio is told in the 



first person, presumably by the spirit of the 
ether, or some loquacious band of waves. The 
effort to sustain an appeal to the imagination 
results in some very silly passages, the worst 
one appearing in the introduction : 

Will the millions and billions of musical scores 
and countless numbers of spoken words ever 
return from the Infinite? Will the waves all roll 
back some day, all intermingled, the music of 
centuries, the works of all composers a hopeless 
jumble, a babel of voices, all so powerful elec- 
trically that the onslaught of invisible waves will 
burn up the ether and radio will be no more? 

The answer is that this catastrophe will posi- 
tively not occur, unless at that time God sees 
fit to suspend the second law of thermodynamics, 
retroactively. 

But, with the exception of some of the chap- 
ter headings and captions, which have no con- 
ceivable relation to the text, this drivel is not 



representative of the contents of Mr. Dunlap's 
book. He is, in point of fact, an old radio man, 
and a Member of the Institute of Radio Engi- 
neers, and when he remembers that there is 
only one inimitable Judge Rutherford, he does 
a good job. What he says is, in the main, ac- 
curate, and jazzed up only within the limits 
permissible in such a book. He has at his fingers' 
ends, or in his scrap book, about all the interest- 
ing things that have ever happened in radio, 
and in "The Story of Radio" relates them for an 
audience to which they will be utterly new. 
The events of the war in the radio field dramatic, 
sos episodes, the old Herald station, OHX, silent 
these fifteen years, all live again in Dunlap's 
pages, and it is pleasing to see their appearance 
in a more or less permanent record. Give the 
book to your son as a birthday present, if you 
have not already bestowed it on him for Christ- 
mas. 

C. D. 



T1 



T2 



LI 



T3 



CX-316-B 
0/-UX216-B 



Xii 



A 

CX-310 
rUX-210 



R1 




CX-310 
orUX-210 



CX-374 
erUX-274 



C1,C2,C3,C4,C5. 



B SUPPLY For 
RECEIVER 



A PUSH-PULL POWER AMPLIFIER 

The amplifier illustrated above is designed to give excellent quality reproduction of radio programs. The push-pull amplifier uses two 
cx-jio (ux-2io) power tubes which are capable of supplying to a loud speaker large amounts of undistorted power. The entire amplifier 

is constructed on a pressed steel sub-base 



A NEW "TWO-TEN" POWER AMPLIFIER 



By William Morrison 



THE combined push-pull power amplifier 
and light socket B power unit described on 
pages 163 and 164 of the July RADIO 
BROADCAST has recreated considerable interest in 
push-pull amplification. The device described 
consisted of a single-stage push-pull power 
amplifier built into a steel case and chassis 
assembly which also housed the power supply 
equipment. The latter furnished A, B, and C 
power to the push-pull amplifier and B power 
for the radio receiver as well. While this unit, 
termed for simplicity a "Unipac," possessed 
considerable merit, its power output, even with 
a pair of 171 type power tubes, would appear to 
be insufficient for really substantially distortion- 
less reproduction, assuming that from 1.5 to 2 
watts of power is required for good dance music 
volume, and that the amplifying system should 
possess a fairly flat frequency characteristic of 
from 30 to 5000 cycles. 

The undistorted power output obtainable from 
the previously described unit is higher than is 
generally obtained from receiver output stages, 
and, in fact, is greater than is often obtained 
from some of the more popular power packs em- 
ploying a 210 type tube, the operating voltages 
of which are often less than they should be. 

As a result of the interest that has been dis- 
played in this earlier push-pull "Unipac," a 
higher-powered model has recently been de- 
veloped employing a pair of ux-2io (cx-3io) 
type amplifier tubes capable of delivering from 
3 to 4 watts of undistorted power to a good loud 
speaker. It is probably quite safe to say that this 
is one of the most powerful receiving amplifiers 
yet developed for the home constructor, and the 
quality of reproduction it provides is really re- 
markable. After listening to the push-pull 
amplifier of the type described here, the signifi- 
cance of the popular phrase "tube overloading," 
as applied to conventional receiving amplifiers, 
is really brought home. 



This newer combination is illustrated here- 
with, and closely resembles the push-pull model 
previously described. The new "Unipac" con- 
sists of a full-wave rectifier, which may use 
either ux-2i6a (cx-3i6-B) or the new ux-28i 
(cx-38i) type tubes, and a push-pull amplifier 
stage with the two ux-2io (cx-3io) power tubes. 
A good idea of the details of the device may be 
gained from the detailed circuit diagram, in which 
the parts are lettered to agree with the list of 
parts on the next page. 

The power supply uses a large, full-wave 
power transformer supplying 7.5 volts from 
two separate windings for lighting the rec- 
tifier and amplifier tubes. Its priimary is 
designed for 105- to i2o-volt, 6o-cycle, lighting 
circuits, while a split high-voltage secondary 
supplies 550 volts a.c. (r.m.s.) to the plates of the 
rectifier tubes. Due to good transformer design, 
the ux-2i6-e (cx-3i6-s) rectifier tubes will 
deliver from 500 to 530 volts of unfiltered d.c. at 
a 106 mA load. This voltage is about all that 
may safely be used upon 210 type amplifier tubes 

Facts About This Amplifier- 

Circuit: Single stage push-pull power ampli' 
fier 

Tubes, TWOCX-JIO (ux-2io) tubes in push- 
pull amplifier, two cx-;i6-B (ux-n6-B) 
rectifiers, one ex -374 (ux-274) glow tube. 

Cost: $83.25, without tubes. (Tubes: $38.50) 

This power amplifier is capable of supplying 
3 to 4 watts of undistorted power to a loud 
speaker. Complete A, B, and C power is ob- 
tained directly from the light socket. The 
rectifier and filter system are designed to 
supply the power amplifier tubes with about 
500 volts for the plate and the necessary C 
bias. The unit is arranged to replace the 
second audio stage in a receiver. The unit is 
encased in a nicely finished metal cabinet 



after a 4O-voIt drop has been allowed for in thi 
filter system. The filter output is about 460 t< 
490 volts d.c., of which 35 to 40 are used for ( 
bias on the amplifier tubes, the remaining 425 t< 
450 volts being actual plate potential suppliec 
to the push-pull amplifier. The rectifier life wil 
be quite good since each ux-2i6-B (cx-3i6-B 
is called upon to furnish only 53 mA., while thesi 
tubes are actually capable of supplying 65 mA 
A single ux-28i (cx^Si) rectifier would delive 
nearly the same power output as the two 2i( 
type tubes, but the use of a single half-wavi 
rectifier, such as the type 281, is generally to bi 
discouraged as increasing the filtration problem 
and almost invariably resulting in an excessivel) 
high value of hum in the loud speaker. Two 281 
type rectifier tubes, however, will give a highe: 
output than two 2i6-B tubes by about 50 to 6t 
volts, and their use is recommended, not so muct 
because of the increased power output, but be 
cause of their probable longer life due to oxidi 
coated filaments and rather generous design. 

The filter system is substantially the same a: 
is used in the smaller "Unipac," except for th( 
use of looo-volt condensers, which are necessary 
because of the high voltages used. A combinatior 
selective and "brute-force" filter scheme is em- 
ployed, resulting in very good filtration at high 
current values. 

The amplifier stage consists of a split winding 
input transformer with a step-up ratio of 3:1 pel 
tube, and a split winding output transformei 
matching the impedance of the ux-2io (cx-3io) 
amplifier tubes to that of a Western Electric 01 
similar loud speaker at 30 cycles. The overall volt- 
age gain of the amplifier is about 20 to 22 times, 

CONSTRUCTION 

THE construction of the "Unipac" is quite 
simple, involving only the mounting of a 
number of standard parts upon a standard steel 
chassis, the wiring up of these parts, and the 



DECEMBER, 1927 



A NEW "TWO-TEN" POWER AMPLIFIER 



139 





THE POWER AMPLIFIER WHEN COMPLETED 
IS HOUSED IN A METAL CABINET 



final attaching of the cabinet or ventilated hous- 
ing after the unit has been tested. The parts 
needed are listed below: 



POWER AMPLIFIER 



Rectifier Tubes (cx-38[ or ux-a8i 

Optional) $15 .00 

One ux-274 or cx-374 Ballast Tube . 5 . 50 

Two ux-2io or cx-jio Power Tubes 18.00 

$38.50 

The "Unipac" will furnish ample power to a 
radio receiver at 45 and 90 volts with voltage held 
constant by a potential dividing resistance and a 
glow tube voltage-regulator, preventing high 
open-circuit voltages to develop, which might 
damage receiver condensers. The amplifier re- 
places the conventional second audio stage of a 
receiver, the input tipjacks connecting to the 
first audio stage output terminals of the receiver, 
and the loud speaker connecting to the output 
jacks of the "Unipac." 

In operation, all tubes will get quite hot, as 
will the larger Ward-Leonard resistor. This 
is correct, as is a slight warmth noticeable in the 
power transformer core. It is necessary always 
to see that the B minus post is grounded, directly 
or indirectly through a condenser. 

POWER TRANSFORMER 
AND RECTIFIER 

To light socket 
110V.60-AC. 



Ta 328 Super Power Transformer 
LI 331 "Unichoke" ..... 
Ti 230 Push-Pull Input Transformer 
Tj 23 1 Push-Pull Output Transformer 
Five 5 1 1 Tube Sockets ..... 
Ci, C 2 , C 3 , 4, C 6 Type 662 Condenser 

Block ......... 

Rz 65 1 Resistor (Ward-Leonard) Set 
Four Frost 253 Tipjacks .... 

Ri Frost FT64 Balancing Resistance 
Van Doom 66 1 Steel Chassis and Cabi- 

net, with Hardware ..... 
Three Eby Binding Posts (B , +45, 

+90) ........ 

Twenty-Five Feet Kellogg Fabricated 

Hook-Up Wire ...... 



$18.00 
8.00 
10.00 

IO.OO 

2.50 

18.00 

7.00 

.60 

.50 



45 



Unless otherwise noted, all the parts listed 
above are manufactured by Silver-Marshall. 

The tubes required for the operation of the 
"Unipac" are as follows: 

Two ux-2i6-e or cx-3i6-B Half-Wave 




To 

loudspeaker 



45 Neg 



B 

To Set / To A Bat 
liiVolt 
C Battery 

A iyi PUSH-PULL AMPLIFIER 

The circuit of the 171 type push-pull amplifier described in the July, 1927, RADIO BROADCAST is given 
above. This amplifier is capable of delivering about 2 watts of power to a loud speaker 

I 

I 

Power Transformer 
& Rectifier 




Loud 
Speaker 



9045 Neg. 
To Receiver 



TOO 

1 no VAC 

Cord & Plug 
to Light Socket | 



A 210 PUSH-PULL AMPLIFIER 

The circuit diagram of the super-power amplifier described in the article given in this illustration. The 55O-volt transformer, T3, at the right, sup- 
plies the two rectifier tubes with sufficient voltage so that when it is rectified and filtered each of the power amplifiers will receive about 500 volts each. 
A glow tube is incorporated in the circuit to maintain the voltages constant, independent of the load. The loud speaker is fed with energy through 

an output transformer. 



The Listeners' Point of View 

THE DX LISTENER FINDS A CHAMPION 



THE DX hound comes in for a lot of un- 
warranted disparagement. He is viewed 
askance by his more enlightened brethren 
as a benighted soul with a perverse idea of what 
radio ought to be used for. His greatest delight, 
as they picture it, is in attacking his receiving 
set with a screw driver and soldering iron, dis- 
emboweling it and putting it together a different 
way. He is said to prefer the faint whisper of call 
letters from some mission station in heathen 
Africa to hearing the Prince of Wales sing 
Frankie and Johnny from the local station. In 
his defense it has been iterated from time to time 
that his experimenting made radio what it is 
to-day. This vindication seems to us to be still 
a pretty sound one. 

There are two types of DX hounds, the radi- 
cals and the conservatives. The extremists care 
for nothing but distance. They will labor into 
the small hours of the night to pick up the signal 
of a station half a continent away. Their stand- 
ard of reception fidelity is not exacting all they 
ask is that the fis be distinguishable from the 
Ps. Once they have gained their quarry (which 
Mr. Webster describes as "the entrails of the 
prey, given to the hounds") their interest is 
over and they start in pursuit of some other 
station. We are in no special sympathy with this 
hunting breed of DX hound, but we will not have 
it said that he is quite useless. He has forced an 
increase in the range of receiving sets. 

But the conservative hound likes to have a 
little sport with his catch after he's run it down. 
Once he has got a distant station he labors 
patiently at tuning it to shut off all extraneous 
noises. Not until he has the program coming in 
with the clarity of a local one is he satisfied. 
Then, if the program is a good one, he listens to 
it. With the pleasure he experiences from the 
program is an added stimulation in the real- 
ization that he is eavesdropping on a scene tran- 
spiring some hundreds of miles away with no 
connection between him and that remote city 
but some great open space and an assortment 
of ether waves. If a sympathy with his en- 
deavours and an occasional emulation of them 
makes us a DX hound, then we are a DX 
hound. Those who advance the protest that 
radio is now so much a matter of fact that they 
cease to marvel at its wonders present not half so 
good a defense of their attitude as they do a 
confession of their lack of imagination. 

After all, the unique thing about radio is not 
that it brings music into your home the phono- 
graph did that years ago but that it conquers 
distance. It was radio's ability to conquer 
distance that gave it its initial impetus, that 
seized the public imagination and bounded it 
along to an unprecedentedly swift success. It 
seems a bit of the basest ingratitude a sort of 
biting the hand that feeds you for radio to turn 
its back now on the characteristic that gave it 
hirth. And, turning its back on it, it is, what with 
its two latest developments: chain broadcasting 
and wired broadcasting. Chain broadcasting, 
with its extended use of telephone wires has made 
the listener in large cities content to receive his 
distant programs from a station perhaps a few 
blocks away. Wired radio, while it still exists 
only as a rumor, is likely to come any time soon. 
Here the program will he circulated on the 



By JOHN WALLACE 



already existing electric power lines which 
enter almost every civilized household, and the 
program received will have spent no instant of 
its life bounding on an ether wave. This seems 
to us a distinct retrogression, technically at 
least. Of course we do not argue that a trip 
through the ether makes a program any better; 
under present conditions the wired program is 
frequently better in quality. But the one is 
genuinely radio, the other simply glorified 
telephony. In short, wired radio, and, to a lesser 
degree, chain broadcasting, summarily renounce 
the fundamental principle upon which radio was 
founded space annihilation. 

This renunciation seems to us premature. The 
possibilities of radio broadcasting have not been 
completely exhausted. Hardly a score of years of 
experimentation has been completed. Certainly 
the idea is worth a score more. 

It may be very practically objected that 
atmospheric conditions, over which man has 
no control, simply render it impossible to extend 
further the range and reliability of radio re- 
ception. This is practically true. Theoretically 
it is false and since this is a theoretical article 
we will press our point further. A demonstrable 
increase in range has been effected within the 
past few years by increasing the power of 
transmitters and the efficiency of receivers. 
There has been no sign from heaven to indicate 
that this increase has reached its limit. So, 
having utterly no knowledge of the mechanical 
problems of radio, but an unbounded faith in 
the uncanny powers of its technicians we argue 
that they can further perfect it if they try. 
But if interest in long range broadcasting is 
abandoned it's a cinch they won't try. 

Radio's unique contribution to what is drolly 
referred to as the "progress" of civilization is 
the conquering of space. We repeat ourself? As 
a follower of radio programs we are well aware 
that it has made an enormous contribution to 
mankind by making music once again part of 
his daily life. In this role it has been of incalcula- 
ble benefit. However, this role, important as it is, 




DAVID BUITOU'H 

The gifted young conductor of the National 
Concert Orchestra, regularly heard through the 
red network of the National Broadcasting Com- 
pany 



is none the less a secondary one. It is possible 
for a man in his home to survive the evening 
without an after dinner concert, but a man at 
sea on a ship with a hole in it is dependent upon 
radio for his life. The city dweller can go to a 
concert hall when he craves music and entertain- 
ment, but the dweller at a lonely outpost in 
Canada is dependent upon radio for any break 
in the monotony of his existence. A catastrophe 
such as a cyclone or an earthquake may cut off 
wire communication with a devastated area but 
radio may still be able to penetrate and convey 
important, perhaps life saving, messages. Or, 
to cite a fanciful but none the less valid instance 
of the primary importance of radio as a long 
distance agent: in time of war an invading force 
could throttle all wired communication within 
the nation but a few well entrenched trans- 
mission stations could still reach the entire 
populace. 

As we have said, further extension of the 
range of broadcasting, particularly in the face 
of the apparently unsurmountable difficulties 
it has already met, is dependent upon a sustained 
interest in achieving this end. So we think the 
vast army of DX hounds instead of being reviled 
should rather be looked upon as a desirable 
faction and, an important balancing element in 
radio's development. 

While, personally, we are most frequently 
interested in the musical things radio has to 
offer, we look forward to the time when it will 
put us in easy touch with foreign shores. Perhaps 
some further use will be made of short-wave 
broadcasting and reception to this end. There 
would be a kick in that which not even the 
staunchest deprecator of DX could deny. But 
such an entertaining, and indeed instructive, 
state of affairs will not have been reached until 
after we first overcome the not inconsiderable 
distances in our own U. S. If we ever do this it 
will be due to the persistency of the DX hounds. 

What We Thought of the First 
Columbia Broadcasting Program 

SUNDAY, the eighteenth of September, wit- 
nessed the debut of the long heralded 
Columbia Broadcasting System. The even- 
ing of Sunday, the eighteenth of September, 
witnessed your humble correspondent, tear 
stained and disillusioned, vowing to abandon for 
all time radio and all its works and pomps. We 
have since recovered and will go on with our 
story. The broadcast divided itself into three 
successive parts, descending in quality with 
astounding speed. 

PART ONE: THE VAUDEVILLE 
This program came on in the afternoon, after 
a half hour's delay due to mechanical diffi- 
culties a heinous sin in this day of efficient 
transmission, but excusable, perhaps, in a half- 
hour-old organization. This opening program, at 
least, was auspicious. The performers were of 
superlative excellence. Bits from a light opera 
were well sung. A quartet gave a stirring ren- 
dition of an English hunting song. A symphony 
orchestra played some Brahms waltzes. A soloist 
sang"Mon Homme" in so impassioned a fashion 



DECEMBER, 1927 



BAD COMMERCIAL BROADCASTING 



141 



that she must have swooned on the last note. 
Then a dance orchestra concluded the program 
with some good playing. The offerings were of 
such high quality that it was doubly disconcert- 
ing to have them strung together with a shoddy 
'"continuity" especially with such stupid and 
overdone continuity as the "and-now-parting- 
from-Paris-we-will-journey-to-Germany " type. 

Continuity is a device used to bolster up weak 
programs. It is a bit of psychological trickery 
designed to keep the listeners listening even 
while their own good sense tells them that there 
is nothing being offered worth listening to. A 
good steak doesn't need to be served with sauce, 
but there's nothing like some pungent Worcester- 
shire for camouflaging the defects of a bad one. 
The items offered on this afternoon program were 
good enough to serve ungarnished, and were 
cheapened by the introductory blah. 

PART TWO: THE UPROAR 

"Uproar," let us hasten to explain, is Major 
J. Andrew White's way of pronouncing Opera. 
We seek not to poke fun at this announcer; he 
is one of the best we have. (Though we think 
both Quin Ryan and McNamee outdid him in 
the recent fight broadcast). But his habit of 
tacking Rs on the end of words like Americar 
and Columbiar doesn't fit into a high-brow 
broadcast as well as it does in a sports report. 
The Uproar was "The King's Henchmen" by 
Deems Taylor. Evidently no effort was spared to 
make the broadcast notable. A good symphony 
orchestra was utilized, capable singers were 
employed, and Deems Taylor himself was in- 
trusted with the duty of unfolding the plot. But 
after all it was "just another broadcast." Musi- 
cal programs into which a lot of talk is injected 
simply will not work. One or the other has to 
predominate. Either make it a straight recitation 
with musical accompaniment or straight music 
with only a sparing bit of interpretative com- 
ment. 

Mr. Taylor's music for this opera is delightful, 
the singing was admirable, but the total effect 
was disjointed and unsatisfactory. The composer 
outlined the story, but, enthralling as it may be 
on the stage, it was impossible to visualize the 
action with any degree of vividness from his 
words. We felt continually aware that there was 
really no action taking place, and the effort at 
make believe was too strenuous and detracted 
from an enjoyment of the music. It was less 
effective, even, than a broadcast from the 
regular Opera stage. Here the piece is likely to 
be more familiar and it is possible to conjure up 
its pantomime from remembrances of perform- 
ances seen. 

It is our humble and inexpert opinion that 
program designers are barking up a wrong tree 
and wasting a lot of energy in their unceasing 
attempts to fit spoken words into musical pro- 
grams. But if they will persist let us suggest that 
they are going about the job in a blundering way 
with no proper realization of its difficulty. All 
present essays in this line fall into two classes: 
those which attempt to relate starkly the neces- 
sary information in a minimum number of words, 
and those which attempt to give a spurious arty 
atmosphere by the meaningless use of a lot of 
fancy polysyllables. 

Neither method works. The first is distracting 
and effectively breaks up any mood or train of 
thought that may have been induced by the 
music. The fancy language system, besides 
being obviously nauseating, takes up too much 
time. 

Program makers may as well realize soon as 
later that the simple possession of a fountain 
pen doesn't qualify a man for writing "script" 
or other descriptive text. It is a job calling for 



the very highest type of literary ability and one 
that can't be discharged by just anybody on the 
studio staff. The properly qualified writer should 
be able to state the information tersely, but, with 
all the vividness of a piece of poetry. Each word 
he uses must be selected because it is full of 
meaning, and of just the right shade of meaning. 
Any word not actively assisting in building up a 
rapid and forceful picture in the listener's mind 
must be sloughed off. A further complication: 
the words can't be selected because they look 
descriptive in type, but because their actual 
sound is descriptive. Altogether an exacting job; 
it' would tax the ability of a Washington Irving. 
It is highly improbable that a genius at writing 
this sort of stuff will ever appear; the ether wave 
is yet too ephemeral a medium to attract great 
writers. But there is no question that scriveners 
of some literary pretensions could be secured if 
the program builders would pay adequately for 
their services. This they will never do until they 
realize the obvious fact that the words that 
interrupt a program are just as conspicuous as 
the music of the program itself. It is incongruous, 
almost sacrilegious, to interrupt the superb train 
of thought of Wagner or Massenet to sandwich 
in the prose endeavours of Mabel Gazook, 
studio hostess, trombone player and "script" 
writer. 

PART THREE: THE EFFERVESCENT HOUR 
dear ! O dear ! Wbiiber are we drifting ! 

You have all heard the ancient story of the 
glazier who supplied his small son with a sack of 
stones every morning to go about breaking win- 
dows. Comes now a radio advertiser who deals 
in stomach settling salts with a program guaran- 
teed to turn and otherwise sour the stomach of 
the most robust listener. The Effervescent Hour 
was the first commercial offering of the new chain 
and far and away the worst thing we ever heard 
from a loud speaker. We thought we had heard 
bare faced and ostentatiously direct advertising 
before, but this made all previous efforts in that 
line seem like the merest innuendo. The name of 
the sponsoring company's product had been 



mentioned ninety-eight times when we quit 
counting. An oily voiced soul who protested to be 
a representative of the sponsoring company 
engaged with announcer White in sundry badin- 
age before each number, extolling the virtues of 
his wet goods and even going so far as to offer 
the not unwilling announcer a sip before the 
microphone. Stuck in here and there amidst 
this welter of advertising could actually be dis- 
covered some bits of program! But such program 
material it was. First the hackneyed "To 
Spring" by Grieg. Then "Carry Me Back to Old 
Virginia." Next some mediocre spirituals fol- 
lowed by a very ordinary jazz band and culmi- 
nating with a so-called symphony orchestra 
which actually succeeded in making the exquisite 
dance of the Fee Dragee from the "Nutcracker 
Suite" sound clumsy and loutish no mean 
achievement. 

One long interruption occured while special 
messages were given to soda jerkers the country 
o'er, inviting them to enter a prize contest for 
the best encomium to the advertiser's wares. But 
the most aggravating interruptions were the 
frequently spaced announcements: "This is the 
voice of Columbia speaking." This remarkable 
statement was delivered in hushed and rever- 
ential tones, vibrant with suppressed emotion, 
a sustained sob intervening before the last word. 
It was positively celestial. We have given a 
rather complete resume of this program, but it 
may be warranted by the fact that probably not 
a dozen people in the country, beside ourself, 
heard it. No one not paid to do so, as we are, 
could have survived it. Perhaps this indictment 
of Columbia's opening performance is unkind in 
the light of subsequent offerings. Our stomach 
is still unsettled. Furthermore we will not make 
use of any of the Effervescent Hour's salts to 
settle it! 

THIS MONTH'S prize for the ugliest and most 
cacophonous coined name plastered on any 
troup of radio performers is hereby awarded by 
unanimous and enthusiastic vote to wow's pop- 
ular entertainers the Yousem Tyrwelder Twins! 




A FAMILIAR WBZ-WBZA PROGRAM GROUP 

The Hotel Statler Ensemble Group, one of the best of the dinner orchestras in the New England 
territory. From left to right: Helen Clapham, Hazel McNamara, Katherine Stang, leader, and 

Virginia Birnie 



AS IHh 





SEES 



KY f AU 



Drawing by Fran\!yn F. Stratford 



Radio As An Electro-Medical Cure-Ali 



THAT electricity plays a considerable role 
in the physiological functions is a fact well 
known and already extensively investi- 
gated. But outside of the area of verified or veri- 
fiable observations there is, as in every other di- 
vision of science, a penumbra of dubious ideas, 
and beyond that lies what Theodore Roosevelt 
called, in one of the most apt of phrases, the 
lunatic fringe. Roosevelt was concerned with the 
field of politics, but politics have no monopoly of 
lunatics nor knaves. The two are frequently 
coupled. 

1 am forced to these melancholy reflections on 
re-reading a newspaper article which was clipped 
for me during the summer. Under the caption, 
"Metal Lingerie As Radio Shield," it related the 
adventures of an afflicted governess in the radio 
realm. It seems that for years the lady suffered 
from "mysterious burns, bruises, blisters, and 
internal pains," which, of course, the doctors 
were unable to explain or cure. Thereupon a 
learned scientist (non-medical) came to her res- 
cue. He subjected the sick woman to extensive 
tests, including the effect of ultra-violet, infra-red 
and X-rays, as well as short and long radio waves. 
She was very sensitive to all these oscillations 
and the professor decided that they might be 
responsible for her pains. He designed for her 
some metal screen lingerie to act as a shield 
against the nefarious oscillations. The method 
of keeping a ground on this intimate shield, as 
the wearer moves about, is not disclosed. Nor, 
unfortunately, are the results of the treatment 
reported. The article does state, however, that 
the afflicted woman, while previously in hospital 
near a radio station, heard sounds like the wind 
whistling through the shrouds of a ship, she 
would awake in the night with pains in her neck 
and ears, and hear a "dream-like voice." At this 
time she spent ten weeks in an insane asylum 
in the hope of being relieved. 

There she was probably on the right track, and 
the fact that she entered the asylum 
voluntarily indicates some degree of 
insight, with a favorable prognosis if 
the patient came under the care of a 
skilled psychiatrist able to give her 
the requisite attention. She is almost 
certainly a mental case. The fact that 
she was bothered in the tests by elec- 
trical oscillations proves precisely 
nothing. If, as part of her psychosis, 
she was convinced that electrical 
waves made her ill, she would exhibit 
symptoms during any tests in the 
course of which she knew or suspected 
such waves were being generated. 
Even skin maladies may be of hys- 
terical origin; this is the modern ex- 
planation of the "stigmata" which, in 
the Middle Ages, were taken for 
crosses printed on the bodies of certain 
persons by divine intervention, just 
as people might be possessed by devils 
through the machinations of Satan. 
Both beliefs are still firmly held in 
some parts, although their influence 
as a whole has decreased inversely 
with the spread of scientific ideas. 



If radio waves were capable of exerting physi- 
ological, effects professional radio workers -in 
transmitting stations would certainly manifest 
whatever symptoms could result. Spending eight 
hours or more each day in an atmosphere where 
the field strength is many volts per meter, some 
of them, after thirty years, should be lamentably 
corroded in sensitive regions. But 1 have never 
heard of a radio man quitting a transmitting 
station because the waves were hurting him. 
I have seen them quit because they did not like 
the cooking, or the shape of the superintendent's 
nose, or the movies in the near-by town, but not 
one of them ever seemed to realize that Hertzian 
oscillations were whizzing through him at a 
velocity of 186,000 miles a second and might 
cause his vital juices to curdle. This seems to me 
cogent evidence. While many individuals might 
be resistant, surely among some thousand of 
exposures a considerable amount of pathology, 
definitely traceable to the ether waves, would by 
this time have accumulated. As for the pitiably 
feeble emanations a few miles from a station, 
which cannot even be heard until they are 
amplified on a grandiose scale, doing a man any 
harm that chance is about as great as One- 
Eyed Connelly's hopes of becoming President of 
the United States. And the possibility of benefit- 
ing a patient physiologically, save incidentally 
through entertainment or education, is equally 
large. 

But some of the apostles of the late Doctor 
Abrams' medical credo know better. One of them 
relates in a learned journal of his cult the story 
of his efforts to benefit the human race by " Im- 
provement in Electronic Diagnostic and Treat- 
ment Apparati; Broadcasting Electro-Magnetic 
Radio Treatment Waves." He has made his 
diagnostic circuit bigger and better, he feels, by 
adding "amplifying attachments" as follows: 

I. A solenoid with its South attached to the 




"HE SUBJECTED THE SICK WO- 
MAN TO EXTENSIVE TESTS" 



dynamizer and its North connected by wire to 
the head-band electrode of the subject, thence, 
through subject and grounded plates, to a metal 
stob driven two feet into the earth. 

2. The South end of diagnostic set is connected 
to a second metal stob. These stobs are set eight 
or ten feet apart on the magnetic meridian as 
ascertained by the compass. 

3. A small high-frequency machine for in- 
creasing the electric tension to drive all possible 
of the radiant force of disease through the diag- 
nostic set and subject; and to stimulate the sub- 
ject's reflexes so that they will act with their 
highest efficiency. . . . 

What the "stob" part refers to I cannot say. 
The word is not in the dictionary. 
But the Doctor continues: 

Later I added a one-stage radio amplifier to 
the above diagnostic outfit which multiplies its 
findings four times. Instead of carrying the wire 
leading from the last reflexophone to the head 
band of the subject, it is carried to the positive 
side of the one stage radio amplifier's transformer 
and then a second wire is carried from the nega- 
tive side of the amplifier's transformer to the 
head-band electrode on the subject. 

Now comes the actual radio application of the 
idea. A two-stage radio amplifier, according to 
the description, is attached to the "master 
oscilloclast." The electronic treatment is thus 
let loose on the world, first on a small scale: 

In the electric store two doors away we secured 
specimens for electronic examination of four 
people and secured specimens from two people in 
a store in the same building with the treatment 
instruments. We then made electronic examina- 
tions of the six specimens and recorded what in- 
fections those people were carrying. After run- 
ning the instruments some twenty days, we again 
secured specimens from the same people and 
made reelectronic examinations. We found that 
four of the people were negative of their carried 
infections the other two not quite 
negative but their infections had 
greatly reduced, showing that only a 
few more days of broadcasting would 
render them negative. 

These experiments proving to us 
that infections could be destroyed at 
a distance of one hundred fifty (150) 
or more feet through air, brick walls, 
glass doors, windows, etc., we decided 
to broadcast the treatment waves out 
for a mile or more. We had made a 
five-stage radio-transmitting broad- 
casting instrument that multiplied the 
eighteen multiplication, of master ma- 
chine, by fifteen hundred times mak- 
ing a total multiplication of master 
machine twenty-seven thousand 
(27,000) times we then had erected 
a broadcasting aerial on top of a five 
story building and connected by wire 
the instruments, oscilloclast, two-stage 
amplifier, one treatment short circuit- 
ed unit and the five-stage radio- 
transmitter to the aerial. We then 
started up the instrument. Then we 
secured a large radio receiving set 
(with loud speaker) from the electric 
company and set it up in a seven- 
passenger automobile and three of us. 



DECEMBER, 1927 



A CRYSTAL-CONTROLLED STATION 



a skilled electrician and radio mechanic, chauffeur 
and myself, tuned at the curb in front of the elec- 
'tric company and could hear the working of the 
oscilloclast we then drove five squares and 
tuned in and could hear the instrument and at 
intermediate points fora little more than a mile, 
showing that the treatment waves were being 
broadcast a mile or more. 

We then secured specimens for electronic 
examination from a distance of half a block up to 
three miles and from many intermediate points. 
The number of specimens secured from begin- 
ning of broadcasting, from November i, 1926, to 
present date, January 20, 1927, were thirty- 
three. We have found that out of that number 
twenty-three have been made negative the 
balance, ten, have been greatly reduced, showing 
that it will only require a week or ten days further 
broadcasting of the treatment waves to render 
them negative. 

The amplified treatment machines are run by 
batteries that are fed from the electric light 
socket and will last from four to six months; 
otherwise batteries only last a few days. The 
five-stage radio-transmitter is also fitted up with 
a large battery supplied by electric socket and 
it in turn supplies the dry batteries, making the 
apparatus very efficient and durable. 

... In the last six weeks or more, with broad- 
casting outfit we have treated electronically a 
population of fifty thousand (50,000) on an 
average of two hours per day, making a total 
of one hundred thousand (100,000) hours per 
day. If the broadcasting electronic treatment 
waves have rendered negative two-thirds of the 
fifty-thousand (50,000) population and reducing 
the other one-third, as was proven in the thirty- 
three test cases (two-thirds made negative, one- 
third reducing) taken out of the same population 
we can readily see the great benefit and per day 
value to the people. Giving the value of one dollar 
per hour for treatment of each individual (which 
is a low tariff fee) we have a total of $100,000.00 
per day. 

If a transmitter fed from batteries can benefit 
the surrounding population to the extent of 
$100,000. per day, conceive of the value of a 100- 
kw. outfit devoted to the same philanthropic pur- 
pose! Why not make it 10,000 kw., while we are at 
it? Assuming that the professor's present equip- 
ment has a capacity of 20 watts, the io,ooo-kw. 
set would be worth 50,000,000,000. a day to the 
citizens of the United States, on the valuation 
basis assumed in the first place. This is of the 
general order of the amount of business trans- 
acted in the country in a year. It is clear, there- 
fore, that a stupendous wealth producing agency 
is in the hands of the electronic practitioner, 
which, I suppose, makes him feel very bad. 

For my own part, I have some qualms. By 
broadcasting these electronic treatments, the 
learned Doc cures all the people within reach 
of their ailments. But why only the people? 
Any such general specific must also be good for 
animals. Horses will be cured of the blind stag- 
gers, tubercular monkeys will rise from their 
beds, sick cockroaches will report at the office fit 
for work. The rats, pediculi, and bed-bugs 
(Cimex leciularins) may benefit even more than 
human beings, who may thereby be crowded off 
the earth. I hope that the electronic broadcaster 
will consider this aspect of the matter and quiet 
my fears if he can. 

Some Catalogues 

ULLETIN No. i of H. F. Wareing and 
Associates, on Modulator Reactors, will 
prove of interest to some broadcasting 
stations. This company, whose address is 401 
Pereles Building, Milwaukee, Wis., is in the 
business of supplying apparatus and service to 
broadcasting stations. The first bulletin includes 
a discussion of modulator reactor design, and a 
price list of types stated to be suitable for trans- 



mitters from 5o-watt to lo-kilowatt size. The 
corresponding currents for which the chokes are 
built vary from 0.25 to 5.00 amperes, at d.c. 
voltages of 1000-5000. Ten- thirty-, and fifty- 
henry reactors are available. Bulletins on other 
broadcast station equipment are to be issued by 
H. F. Wareing and Associates at intervals, ac- 
cording to the announcement reaching us. 

The Samson Electric Company of Canton, 
Massachusetts, distributes a "Radio Division 
Price List" including, besides the usual radio 
parts sold to receiver constructors, such items as 
microphone input transformers, tube-to-line and 
line-to-tube transformers, mixer equipment, 
and other specialized broadcast transmitter and 
public address material. They have made up a 
blueprint showing a small public address system 
assembled with their parts. Provision is made for 
microphone, radio set, and phonograph pick-up. 
There are three 0.25 ampere (filament) tubes, 
and apparently the output stage is push-pull, 
using 5- or 7.5-watt tubes. On this basis the 
volume capacity should approximately equal that 
of the Western Electric 3-A size P. A. system. 

Design and Operation of Broad- 
casting Stations 

1 8. Pie^o-Electric Control 

THE field of piezo-electric phenomena 
includes the generation of electrical po- 
tentials in various substances by the 
application of physical pressure, and, conversely, 
changes in physical dimensions directly corre- 
lated with electrical conditions. It is not a new 
division of physics; the piezo-electric properties 
of quartz, for example, were investigated by P. 
and J. Curie in 1889. The effect itself was dis- 
covered by the brothers some years earlier. 



Prof. W. G. Cady, about eight years ago, began 
the work which resulted in the application in the 
radio art of crystal frequency control. He re- 
ported his investigation of "The Piezo-Electric 
Resonator" in the Proceedings of the Institute of 
Radio Engineers, Vol. 10, No. 2, April, 1922. 
Oscillating crystals are used as frequency stan- 
dards in wave meters and monitoring units, 
some practical forms much used by broadcasting 
stations being those produced commercially by 
the General Radio Company. RADIO BROADCAST 
has printed two comprehensive articles by M. T. 
Dow on crystal circuits and measurement ap- 
plications (January and September, 1927). A 
direct form of frequency control of particular in- 
terest to broadcasters is that in which the trans- 
mitter functions as a radio-frequency amplifier, 
the master oscillator being a crystal-controlled 
tube. Some recent engineering publications on 
this aspect include three in the I. R. E. Proceed- 
ings: A. Crossley: "Piezo-Electric Crystal- 
Controlled Transmitters" (Vol. 15, No. i, Jan., 
1927); A. Meissner: "Piezo-Electric Crystals at 
Radio Frequencies" (Vol. 15, No. 4, April, 1927); 
and H. E. Hallborg: "Some Practical Aspects" of 
Short- Wave Operation at High Power" (Vol. 15, 
No. 6, June, 1927). In the present article an 
attempt will be made to introduce the subject to 
broadcast operators who have not worked with 
crystal-controlled transmitters so that when 
they are called on to operate such equipment 
they will be in possession of some of the elemen- 
tary facts. 

In itself the use of a crystal is no guarantee of 
frequency stabilization to any required degree of 
accuracy. Some broadcasters seem to believe 
that the use of a crystal in almost any kind of 
holder, with some sort of radio-frequency am- 
plifier following, will insure constant frequency 
radiation. Actually a crystal is of little use unless 




Choke 



Main Plate Supply 



THE CIRCUIT DIAGRAM OF A CRYSTAL-CONTROLLED TRANSMITTER 
In actual practice, tubes A and B in the third stage generally consist of two banks of power tubes. 
The filaments of only one set of tubes are lighted and they deliver power to the antenna circuit while 
the other bank, with the filaments not lighted, acts as a neutralizing circuit to prevent the active bank 
from breaking into self oscillation. In operation, if an accident happened to the active bank, the fila 
ments could immediately be turned off and the filaments of what was the inactive bank turned on. 
The latter bank of power tubes would then deliver power to the antenna while the other bank func- 
tioned as a neutralizing condenser 



144 



RADIO BROADCAST 



DECEMBER, 1927 



very specific and delicate conditions of operation 
are maintained for it. 

A piezo-electric substance for radio crystal 
control purposes must have certain internal 
atomic properties, and it must be hard, durable, 
and not easily broken down physically or electric- 
ally. Quartz is the best commercial product so 
far offered to fill these requirements. The manu- 
facture of quartz crystals for radio purposes is a 
specialized subject and, as few broadcasters are 
likely to attempt grinding their own crystals, 
need not be discussed here. The crystal should 
be optically ground to oscillate at only one fun- 
damental frequency. If the frequency is to remain 
constant, the crystal must be maintained under 
constant physical conditions as a prerequisite. 
This includes an unvarying contact pressure and 
temperature. When the temperature changes the 
dimensions of the crystal change and the natural 
frequency varies proportionately. The crystal 
must be kept clean; a drop of oil or water in- 
troduced between the holder and the quartz 
slab will usually stop oscillations altogether. It 
follows that in a broadcasting station installation 
the crystals are usually kept in a dust-proof box 
whose temperature is thermostatically controlled. 
Some commercial crystals, in addition, are sealed 
into small individual containers, provided with 
lugs designed to slip under binding posts. The 
actual contact with the crystal is inside the con- 
tainer. If springs or screw clamps are used to 
make contact with an open crystal care must be 
taken, to secure parallel movement of the metal 
surfaces, so that the crystal is not subjected to 
pressure on part of its surface and left untouched 
elsewhere. A loose contact leads to brushing, 
heating, and possible cracking of the crystal. The 
capacity of the crystal holder should be small 
in order that its piezo-electric variations may 
exert the maximum governing effect on the cir- 
cuit of which the crystal is a part. It will be noted 
that there is some design analogy between the 
old-style crystal detector stand and the quartz 
crystal holder of a modern tube transmitter; 
each has protean forms. Some illustrations of 
actual crystal holders will be found with the 
RADIO BROADCAST papers mentioned in the 
bibliography, and Crossley includes a detailed 
description of the contact requirements in his 
paper. 

The radio-frequency energy in the initial 
crystal circuit may amount to a fraction of a 
watt, while the final stage may deliver many 
thousand watts to the antenna. It is clear that 
great care must be taken to prevent feed-back, 
parasitic oscillations, and unstable circuit con- 
ditions along the line. Under some conditions of 
circuit imbalance the crystal is likely to overheat 
and be damaged. The transmitter may stop oscil- 
lating. In the endeavor to control regeneration 
and secure circuit stability, designers have fre- 
quent recourse to shielding and neutralization of 
successive amplifier stages, and sometimes push- 
pull radio frequency amplification is employed, 
resulting in a series of balanced circuits anal- 
ogous to those of low frequency telephone 
practice. 

In a crystal-controlled telephone transmitter, 
modulation may take place in the final stage or 
at an intermediate point after the crystal but 
before the final stage. The advantage of modu- 
lation at a low power level lies in the possibility 
of securing ample modulator capacity relative to 



the radio frequency energy to be modulated. 
But if, for example, modulation takes place in 
one of the earlier stages at a power level of, say, 
50 watts, care must be taken not to impair the 
audio-frequency characteristic of the transmitter 
by cutting of the side bands in successive tuned 
stages, and of course the power tubes must have 
sufficient capacity to handle the peaks of modu- 
lation. The Bell Telephone Laboratories engin- 
eers seem to incline toward low power modula- 
tion, while the Westinghouse and General Elec- 
tric engineers prefer to wait until the full radio 
frequency power is developed before impressing 
the audio frequency on the carrier. 

The power of successive stages depends on 
tube characteristics and the use to which the 
transmitter is to be put. Crossley shows a i 50- 
6oo-kc. telegraph transmitter in which the 
crystal controls a y.j-watt tube, which is followed 
by a 5O-watt impedance-coupled amplifier, a i- 
kw. tuned amplifier stage, and the final 2o-kw. 
stage feeding the antenna. These figures and 
some others in this paragraph represent the 
nominal oscillator ratings of the tubes in ques- 
tion; the powers actually developed are generally 
less. Meissner mentions a telephone transmitter 
in which, after the crystal tube, 5-watt,75-watt, 
joo-watt, and j-kw. stages are found, the last 
named supplying 3 kw. to the antenna. The Na- 
tional Broadcasting Company's Bound Brook 
telephone transmitter (made by Westinghouse for 
R.C.A.) uses a y.j-watt tube in the crystal stage, 
swinging a 2jo-watt tube, followed by two 250*5 
in parallel (500 watts) before the final 4O-kw. 
bank. Bellmore, built by General Electric for the 
N. B. C., uses more stages; the crystal, likewise 
governing a y.j-watt tube, is coupled to another 
of the same size; then follow a 5o-watter, two 
fifty-waiters in parallel (100 watts), a looo-watt 
tube, a single 2o-kw. tube run at about a quarter 
of its rating, and the final jo-kw. stage. In both 
of these American transmitters, plate modulation 
of the final power stage is used. In the Bellmore 
transmitter the output of the crystal stage is 
purposely kept low as one of the design consider- 
ations, only about 0.5 watt being generated, 
while Crossley mentions getting 21 watts from a 
crystal-governed tube of the same type, in one 
of the U. S. Navy experiments. This divergence 
shows how design calculations determine operat- 
ing conditions. 

Fig. i is a schematic circuit diagram of a 
crystal-controlled telephone transmitter without 
the audio amplifier and the power supply to the 
modulator and r. f. output stage. The power rat- 
ings of the successive stages have been omitted 
because, as indicated above, various sizes of 
tubes might be employed in such a chain, ac- 
cording to the final output required, the tube 
characteristics, and other design factors. 

The Small Broadcaster 

IN A letter of some length, which we should 
print in full if the space were available, Mr. 
Robert A. Fox, formerly owner and manager 
of Station WLBP of Ashland, Ohio, takes me 
severely to task for my past animadversions on 
incompetent broadcast technicians, which he ap- 
parently thinks were aimed exclusively at small 
stations, and then goes on to a penetrating dis- 
cussion of the small stations' economic problems. 



Mr. Fox points out that in arranging high 
quality programs the small station is at a dis- 
advantage, "for the simple reason that musicians 
do not charge you for their time according to the 
power of your station, but in accordance with 
the number of hours required of them." The ad- 
vertiser, on the contrary, will pay more or less 
proportionately according to the power. The 
members of the station staff are in the same posi- 
tion as the musicians. The result is that one man 
must sometimes assume the staggering burden 
of acting as "station monitor operator, an- 
nouncer (doing a nemo job of it), operator; chief 
engineer as well as salesman, financier, publicity 
agent, and program director," all this with one 
assistant. Even then the structure collapses under 
the fixed expense, and Mr. Fox concludes, "The 
small broadcaster is economically doomed." 
But, he insists, the failure is economic, not per- 
sonal "the fellows who have been operating 
under 1000 watts have more brains than those 
above 1000 watts." 

They may not have more brains nature does 
not distribute brains according to antenna watts, 
either in direct or inverse ratio but they cer- 
tainly have more courage. And, while economic- 
ally they may be sick, they may yet survive, on 
some other basis, to see a better day, No one can 
say, at this juncture, that the small neighbor- 
hood station will not find a place in community 
life, with some form of cooperative support, in a 
frequency band wherein it can serve local in- 
terests without interfering with the large stations 
and networks aspiring to national coverage, and 
be in turn protected from interference by them. 

As to the less material matter of my own atti- 
tude toward such enterprises, it is a curious 
commentary on our American attitude toward 
criticism in general that when a man states 
baldly, in public, unpleasant facts about institu- 
tions or people, he is immediately suspected of 
being hostile to those institutions and people. 
That it is his right and duty, once he has set up 
as a critic, technical or social, to discriminate be- 
tween what he finds good and bad, is a basic fact 
not sufficiently recognized among us, in radio and 
elsewhere. There is still a lot of bad broadcasting 
and incompetent operation going on. No one 
with a pair of ears and the tonal discrimination 
of a tomcat can think otherwise. There is also a 
large and growing element of good showmanship, 
efficient operation, and skilled personnel, among 
both large and small stations, and 1 have not 
been backward in giving credit to those responsi- 
ble for such progress. The standards have been 
lower among smaller stations, because of the lack 
of resources and, sometimes, because of the lack 
of time and skilled personnel. All these factors go 
together. If a man tries to act as announcer, 
engineer, operator, program director, and publi- 
city representative of a station he will inevitably 
turn out a half-baked job in each capacity. He 
may be a hero, but he is not a broadcaster by 
1928 standards. One may admire his courage 
and still tell him what one thinks of his audio 
frequency band and the quality of his sopranos. 
As for constructive contributions, I have tried 
to do my part by writing technical articles which 
are of use largely to the smaller broadcasters, be- 
cause the information contained in them is com- 
mon property among the operators of the bigger 
stations. Let that be weighed against my refusal 
to be a member of a cheering squad. 



RADIO BROADCAST ADVERTISER 



145 



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146 



RADIO BROADCAST ADVERTISER 



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The Radio Broadcast 



SHEETS 



THE RADIO BROADCAST Laboratory Information Sheets are a regular feature of this 
magazine and have appeared since our June, 1926, issue. They cover a wide range 
of information of value to the experimenter and to the technical radio man. It is not out 
purpose always to include new information but to present concise and accurate facts in 
the most convenient form. The sheets are arranged so that they may be cut from the 
magazine and preserved for constant reference, and we suggest that each sheet be cut out 
with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should 
be arranged in numerical order. An index appears twice a year dealing with the sheets 
published during that year. The first index appeared on sheets Nos. 47 and 48, in No- 
vember, 1926. In July, an index to all sheets appearing since that time was printed. 

All of the 1926 issues of RADIO BROADCAST are out of print. A complete 
set of Sheets, Nos. I to 88, can be secured from the Circulation Department, 
Doubleday, Page & Company, Garden City, New York, for Si oo Some readers have 
asked what provision is made to rectify possible errors in these Sheets. In the unfor- 
tunate event that any such errors do appear, a new Laboratory Sheet with the old 
number will appear. 

THE EDITOR. 



No. 145 



RADIO BROADCAST Laboratory Information Sheet December, 1927 

Loud Speakers 



GENERAL CONSIDERATIONS 

nHAS been realized for some time that a large 
u iaphragm type of loud speaker is capable of giving 
somewhat better frequency response than can be 
obtained from a short horn. 1 hese large diaphragm 
loud speakers have generally been called cones 
because the large diaphragm in most cases takes 
the form of a right circular cone. 

There are certain essential characteristics which 
must be striven for in designing a loud speaker of 
this type. ^ hat we desire in the diaphragm is to 
obtain a large surface of great stiffness or rigidity 
and, at the same time, extreme lightness. If such a 
material can be obtained, a very satisfactory loud 
speaker could be made consisting simply of a sheet 
of the material freely supported at the edge. Such 
a material having a high ratio of stiffness divided 
by mass is difficult to obtain, and it has been neces- 
sary to devise diaphragm shapes which will give the 
necessary stiffness and which will still be light. This 
is the reason why a cone shape has generally been 
used, for it will give the necessary characteristics. 

Recently there was described in RADIO BROAD- 
CAST the Balsa wood loud speaker, which repre- 
sents an attempt to obtain a large flat diaphragm 
using a light material, with the required stiffness 
obtained through the use of slats radiating from 



the center. Because of the extreme lightness of Balsa 
wood it is possible to obtain in this way a very high 
ratio of stiffness to mass. 

It is, of course, essential that any loud speaker, 
if it is to radiate sound effectually, be made as light 
as possible so as to require only a small amount of 
energy to move it. It is desirable that the entire 
diaphragm shall move and that the major resis- 
tance it encounters, in moving should be that due 
to the energy required to move the air about the 
diaphragm and set up sound waves in the air. 
Any of the available energy that is used for other 
purposes represents a loss. 

An excellent book, WiVr/rss Loud Speakers, is 
published in England by Iliffc and i;ons and writ- 
ten by N. W. McLachlan. The author says, in 
speaking of cone type loud speakers: 

"There is a wide field for rrathematical and ex- 
perimental work regarding the behavior of dia- 
phragms of various shapes and sizes. By exact 
measurement, coupled with analysis, it will be 
possible to pave the way to better reproduction 
and to evolve a diaphragm with qualities superior 
to those now used. Until this is done we must re- 
main in ignorance of the action of diaphragms at 
various frequencies. The human ear may judge one 
diaphragm to be better than another, but it cannot 
give exact data." 



No. 146 RADIO BROADCAST Laboratory 

B Power Device Ch 

TYPICAL CURVES 

f\N THIS Laboratory Sheet are given a group 450 
v of curves, supplied by the Raytheon Manu- 
facturing Company, which show how the output 
voltage of a typical B power unit varies with the 400 
transformer voltage. The circuit diagram of the 375 
rectifier and filter system used in making these 
tests is given on the curve. The curves apply when 350 
a type BH or similar tube is used as the rectifier. ... 
These curves indicate the following facts: 
(A.) That the slope of all of the curves is the 300 
same. This is to be expected because the u ... 
slope is determined entirely by the resis- 
tance of the circuit, which docs not vary. 250 
(B.) That an increase of 50 volts in the trans- g 
former voltage is effective in producing an ,- ' 
average of 75 volts increase in the output 200 
voltage. g 176 
(c.) That the output voltages of the system 
at no load have approximately the same 150 
value as the transformer voltages. 125 
(D.) That the total resistance of the rectifier- 
filter system is about 1340 ohms. (This 100 
value is determined by dividing the dif- 
ference of any two voltages on the straight 
portion of any one curve by the differ- 50 
encc of the corresponding load currents.) 25 
The resistance of the choke coils used was 


information shee! December, 1927 
laracteristics 


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51 


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Voltage either 
side of Trans, 
rve CenlerTap 
A 200 
B 25C 
C 300 
D 350 


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known to Ix; 600 ohms so lliat tin 1 elfcv- 10 2 o so 40 50 60 70 80 90 100 
tive resistance of the rectifier is about LOAD IN MILLIAMPERES 
740 ohms. 



RADIO BROADCAST ADVERTISER 



147 




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148 



RADIO BROADCAST ADVERTISER 



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H. B. 12-27 



No. 147 



RADIO BROADCAST Laboratory Information Sheet December 1927 



"Gain" 



SIMPLE MATHEMATICAL CALCULATION 7 



'"PHE diagram on this Sheet shows an ordinary 
* tuned circuit with a source of high-frequency 
voltage, e, in series with it. The voltage e can be 
considered to be the voltage induced in the tuned 
circuit from another coil, the primary of a radio- 
frequency transformer for example. This voltage 
will cause a current to flow in the tuned circuit 
and the ratio of the voltage E, developed across 
the entire circuit, to the voltage e, induced in the 
circuit, is known as the "gain" of the tuned circuit. 
The more efficient the tuned circuit is, the greater 
will be the "gain." We will now derive a mathe- 
matical expression for the "gain" of a tuned circuit. 
The current, I, flowing in a tuned circuit at re- 
sonance is: 



K 

where e = the voltage induced in the circuit and 
R = resistance of the circuit. The current flowing 
through the inductance coil, L, generates a potential 
across the coil, determined as follows: 

E = wLI (2.) 

where d> = 6.28 times the frequency of the current, 
L = inductance of coil in henries, and I has the 
same meaning as in equation (1.) Substituting in 
equation (2.) the value for I given in equation (1,) 
we have: 



and dividing through by e we get: 



But, as stated previously, the ratio of E to e is 
the gain of the circuit. Therefore: 



,, . 
Gam = 



(4.) 



This final expression indicates that, to obtain 
greatest efficiency from a tuned circuit, it is essen- 
tial that the ratio of the inductance reactance (toL) 
to the resistance of the coil should be made as large 
as possible. 



E = 



(3.) 



No* 148 RADIO BROADCAST Laboratory Information Sheet December, 192? 



An A. C. Audio-Frequency Amplifier 



WHAT PARTS TO USE 

'"PHE introduction of the new a. c. tubes makes 
-* possible the construction of an a. c. audio 

amplifier with the necessary A, B, and C voltages 

supplied directly from the light socket. The list 

of parts necessary to construct such an amplifier 

is given on this Sheet. The circuit diagram is given 

on Laboratory Sheet No. 149. 

An amplifier of this type is well suited for use 

with a small receiver consisting of one or more stages 

of radio- frequency amplification and a detector. 

The circuit has been so designed that B voltages 

for the r. f. and detector tubes can be obtained 

from the audio amplifier device. 

The following parts are necessary to construct 

this amplier: 

A A. C. Tube, Type ux-226 (cx-326) or Equiva- 
lent. 

B ux-171 (cx-371) or Equivalent. 

TI, TT Two High-Quality Audio Transformers. 

Ts Filament-Lighting Transformer to Supply 
Tube A. 

T^ Power-Supply Transformer Designed for use 

in 171 Type B Power Units. 



Li, L-r Filter Choke Coils. 
Ls Output Choke Coil. 
Ci, G> 1-Mfd. Bypass Condensers. 
C 3 , C* 2 Mfd. Filter Condensers. 
Cs 4-Mfd. Filter Condenser. 
C 6 , C 7 , Cg 1-Mfd. Filter Condensers. 
Cfl 2-4-Mfd. Fixed Condenser. 
RI 30-Ohm Center-Tapped Resistance. 
Rs 1500-Ohm Fixed Resistance Capable of Carry- 
ing 4 mA. 

R; 2000-Ohm Fixed Resistance Capable of Carry- 
ing 20 mA. 

R4 -Tapped Resistance for Use in Output of B 
Power Units. 

In wiring this amplifier, be sure to twist the fila- 
ment leads to the two tubes, to prevent hum. C 
bias for the first tube, A, is obtained from resis- 
tance Ra, and resistance Rj supplies the output 
tube with grid bias. 

The input terminals of the amplifier should con- 
nect to the output of the detector tube, terminal 
No. 1 connecting to the plate and terminal No. 2 
to the detector B plus. 

To prevent hum it is essential that the negative 
B be carefully grounded. 



No* 149 RADIO BROADCAST Laboratory Information Sheet December, 1927 

Circuit Diagram of an A. C. Audio Amplifier 




Here is the circuit diagram of an alia. c. audio amplifier. The list of parts is given on Sheet No. 148. 



RADIO BROADCAST ADVERTISER 



149 




Silent 
Magic 



Here ia the Evereody 
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No. 486, Eveready's 
longest-lasting provider 
of Battery Power. 



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cabaret, a church, or what- 
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and your attentive ear does 
the rest. That is all there is 
to this magic of radio. 

Or almost all. If a radio 
set is to work at its very best, 
attracting no attention to 
itself, creating for you the 
illusion that can be so con- 
vincing, you must pay a 
little attention to the kind 
of power you give it. There 
is but one direction, a 
simple one use Battery 
Power. Only such power is 
steady, uniform, silent. It is 
called by scientists pure 
Direct Current. Any other 
kind of current in your 




Radio Batteries 




Radio is better with Battery Power 



-they last longer 



radio set may put a hum 
into the purest note of a 
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of the greatest singer, a 
rattle into the voice of any 
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Don't tamper with tone. 
Beware of interfering with 
illusion. Power that reveals 
its presence by its noise is 
like a magician's assistant 
who gives the trick away. 
Use batteries use the Ever- 
eady Layerbilt "B" Battery 
No. 486, the remarkable 
battery whose exclusive, 
patented construction makes 
it last longest. It offers you 
the gift of convenience, a 



gift that you will appreciate 
almost as much as you will 
cherish the perfection of 
reception that only Battery 
Power makes possible. 
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Night 9 P. M., Eastern Standard 

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WWJ Detroit 
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t. Paul 

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air is full of things you should n't miss 



150 



RADIO BROADCAST ADVERTISER 



tomatic rower 
Gbntfo 




FOR 
CHRISTMAS 

The gift of gifts for the 
set owner. 

Makes radio more con- 
venient because it hand- 
les the switching of the 
trickle charger and B 
eliminator automatic- 
ally. Controls charger 
or eliminator separately 
or both in combination. 

When the set is turned 
on the trickle charger is 
cut out and the B elim- 
inator is switched in. 
When the set is turned 
off the trickle charger is 
cut in and the B elim- 
inator is switched off. 

Better reception and 
greater satisfaction are 
assured. The A battery 
is charging when the set 
is not in use. It is always 
ready with plenty of 
kick when the set is 
turned on. The B elim- 
inator is on only when 
the set is in use; the 
tubes last longer and 
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there is no waste of 
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No. 150 



RADIO BROADCAST Laboratory Information Sheet 

Oscillation Control 



December, 1927 



THE USE OF NEUTRALIZATION 

TT HAS been pointed out many times that an or- 
* dinary three-element tube has an inherent ten- 
dency to oscillate due to the feed-back that occurs 
from the plate circuit to the grid circuit through the 
grid-plate capacity, indicated by dotted lines in 
the accompanying diagram. This diagram repre- 
sents the circuit of a single-stage of tuned radio- 
frequency amplification, using the Rice system of 
neutralization, and the following explanation will 
make clear why the tube tends to oscillate and why 
the tendency to oscillate can be overcome by using 
some system of neutralization. 

When a tube acts as an amplifier, the voltage 
developed in the plate circuit is greater than the 
voltage originally impressed on the grid circuit 
and, consequently, if the plate circuit is coupled 
to the grid circuit in any manner whatsoever, cur- 
rent will tend to flow from the point of high poten- 
tial, that is the plate, to a point of lower potential, 
in this case the grid. If this current flowing to the 
grid circuit has the same phase as the original sig- 
nal impressed on the grid, then the grid voltage 
will become somewhat greater and will be equal to 
the original signal in the grid circuit plus the volt- 
age induced in the grid circuit from the plate. An 
increase in the grid voltage again produces an in- 
crease in plate voltage which in turn reacts back 
on the grid until the voltage is increased to a point 
where the losses in the circuit are overcome, and 
then the tube breaks into continuous oscillation. 

It should be evident that if we can place in the 
circuit some device that will impress a potential 



on the grid kind ot an eqisjal and opposite to that 
caused by the coup'mg between the grid and 
plate, then the resu.tant effect will be zero and 
the tendency for the circuit to build up and break 
into continuous oscillatkwi will be nullified. The 
Rice system of neutralization is one way of doing 
this, the circuit foi which is shown in the accom- 
panying diagram. The grid-plate capacity is ^hown 
in dotted lines and this is the capacity through 
which current flows from the plate to the grid cir- 
cuit and which ordinarily ca\Bes the tube to oscil- 
late. This caoacity is neutralized in the Rice sys- 
tem by connecting condenser Cn as indicated. 

Grid Plate Capacity 
; ir- 




No. 151 



RADIO BROADCAST Laboratory Information Sheet December. 1927 



Single-Control 



BOOSTING SENSITIVITY 



LABORATORY Sheet No. 33, October, 1926, 
some facts were given regarding the tandem 
tuning of several condensers, to decrease the number 
of controls. It was pointed out that, to obtain 
single control, it is necessary to overcome the 
effect of the antenna circuit in some manner, 
and that a common method of doing this is as in- 
dicated in sketch A on this Sheet. The owner of a 
receiver of this type may greatly increase its sen- 
sitivity by connecting a variometer between the 
antenna and ground posts as indicated in sketch 
B. This, of course, adds one more control to the set 
but in those cases where greater sensitivity is neces 
sary, the additional control is justified. 

The increase in sensitivity that results when the 
variometer is used in the antenna circu't is due to 
the fact that it brings the antenna into resonance 
with the signals being received and the resultant 
gain in amplification is practically equal to that 
which would be obtained from an additional stage 
of radio- frequency amplification. 

In some cases when thir, variometer is usea, i- 
will be found that the receiver tends to oscillate, 
or actually does oscillate, when all of the circuits 
are brought into resonance. Fortunately, however, 
most single-control receivers have a volume control 
in the radio- frequency system and it will be found 
that, by cutting down the volume control, :. ooint 
will be reached where the set will stop oscilliting 
and usually the actual volume obtained with the 
antenna circuit tuned will be rrnch greater than 



that obtained before with the volume control turned 
to the "maximum" position. The tendency of the 
circuit to oscillate can also be lessened by some- 
what decreasing the r. f. plate voltage. 



Ist.R.F. 



2nd. R.F. 




No. 152 



RADIO BROADCAST Laboratory Information Sheet December, 1927 



Speech 



SOURCES OF INFORMATION 



nature of speech has be?n the subject of 
many scientific inquiries and many of the in- 
vestigations in connection with speech have been 
recorded in various scientific journals. 

Back in 1873, Alexander Graham Bell, familiar 
to us as the inventor of tne telepnone, did con- 
siderable work in analyzing speech and in "de- 
vising methods of exhibiting the vibrations of 
sounds opticallly," and much of the recent research 
has been done by engineers and physicists associated 
with the laboratories of the telephone companies. 

A bibliography is given below of some of the im- 
portant articles and books on the subject with 
which we are familiar. This bibliography is by no 
means complete in itself but if the references given 
are studied it will be found that some of them con- 
tain many references to other papers on the sub- 
ject. I. B. Crandall's article, in the October, 1925, 
Bell System Technical Journal, in particular, con- 
tains about twenty-six references to other sources 
of information on speech and related subjects. 

REFERENCE SOURCES 

Bell System Technical journal 

C. F. Sacia and C. J. Beck; "The Power of Fun- 
damental Speech Sounds." July, 1926. 



I. B. Crandall: "Sounds of Speech." October, 
1925. 

C. F. Sacia: "Speech Power and Energy." Oct- 
ober, 1925. 

Irving B. Crandall: "Dynamical Study of the 
Vowel Sounds." January, 1927. 

C. R. Moore and A. S. Curtis: "An Analyzer 
for the Voice Frequency Range." April, 1927. 

Journal of the American Institute of Electrical 
Engineers 



Jones; "The Nature of Language." April, 1924. 

Martin and Fletcher: "High-Quality Transmission 
and Reproduction of Speech and Music:" March. 
1924. 

Maxfield and Harrison: "Method of High 
Quality Recording and Reproducing of Music and 
Speech Based on Telephone Research." March, 

Books 

Miller: Science of Musical Sounds. Second Edi- 
tion. Macmillan. 

Sabine: Collected Papers on Acoustics. Harvard 
University Press. 



RADIO BROADCAST ADVERTISER 



151 




great improvements 
in radio power have been 




TJ || - _ 

Balkite 



A Contains no bat- 

A ftrj , The ,. m e 



as Ballcite " AB," but for the " A"circuit 
only. Enables owners of Ballcite "B" to 
make a complete light socket installa- 
tion at very low cost. Price $35.00. 




Rallcite "B" 

JjaiKllC Lt est i, ve j devices 
in radio. The accepted tried and proved 
light socket "B" power supply. The 
first Balkite "B," after 5 years, is still 
rendering satisfactory service. Over 
300,000 in use. Three models: "B"-W, 
67-90 volts, $22.50; "B"-i35,* 135 
volts, $35.00; "B"-i8o, 180 volts, 
$42.50. Balkite now costs no more than 
the ordinary "B" eliminator. 




Balkite Chargers 

Standard for ''A" batteries. Noiseless. 
Can be used during reception. Prices 
drastically reduced. Model "J,"* rates 
2.5 and .5 amperes, for both rapid and 
trickle charging, $17.50. Model "N"* 
Trickle Charger, rate .5 and .8 am- 
peres, $9.50. Model "K" Trickle 
Charger, $7.50. 

*Spedal models for 25-40 cycles at 
slightly higher prices. Prices are higher 
West of the Rockies and in Canada. 




THIRST noiseless battery charging. 
i Then successful light socket "B" 
power. Then trickle charging. And to- 
day,mostimportantofall,Balkite"AB," 
a complete unit containing no battery 
in any form, supplying both "A" and 
"B" power directly from the light sock- 



radio dealer Balkite is a synonym for 
quality. 

Because the electrolytic rectification 
developed and used by Balkite is so re- 
liable that today it is standard on the 
signal systems of most American as well 
as European and Oriental railroads . It is 

et, and operating only while the set is this principle that does away with the 
in use. The great improvements in ra- necessity of using tubes for rectifying 
dio power have been made by Balkite. current that makes all Balkite Radio 



The famous 
Balkite electrolytic principle 

This pioneering has been important. 
Yet alone it would never have made Bal- 
kite one of the best known names in 
radio. Balkite is today the established 
leader because of Balkite performance 
in the hands of 
its owners. 

Because with 
2,000,000 units 
in the field Bal- 
kite has a record 
of long life and 
freedom from 
trouble seldom 
equalled in any 
industry. 

Because the 
first Balkite "B," 
purchased 5 years 
ago, is still in use. 
Because to your 




"AB" Contains no battery. 
A complete unit, replacing both "A" and "B" bat- 
teries and supplying radio current directly from 
the light socket. Contains no battery in any form. 
Operates only while the set is in use. Two models: 
"AB" 6-135,* 135 volts "B" current, $64.50; 
"AB" 6-180, 180 volts, $74.50. Special model for 

Radiola 28, $63.50. 



Power Units, including the new Balkite 
"A" and "AB," permanent equipment 
with nothing to wear out or replace. 
Balkite has pioneered but not at 
the expense of the public. 

Radio power 
with batteries or without 

Today, whatever 
type of radio set 
you own, what- 
ever type of pow- 
er equipment you 
want (with bat- 
teries or without) 
Balkite has it. 
And production 
is so enormous 
that prices are as- 
tonishingly low. 
Your dealer will 
recommend the Bal- 
kite equipment you 
need for your set. 



FANSTEEL PRODUCTS COMPANY, INC., NORTH CHICAGO, ILLINOIS 



Licensees for Qermany: 

Siemens & Halske, A. G. Wernerwerk M 
Siemensstadt, Berlin 



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RdJlSTEEL 1 

Balkite 

o Tower Units 



152 



RADIO BROADCAST ADVERTISER 



Perfect Radio Parts 

for Discriminating 

Set Builders 



The BRADLEYUNIT-A 




is a fixed resistor that is molded and 
heat-treated under high pressure. It 
does not rely on glass or hermetic 
sealing for protection against mois- 
ture. Is not affected by temperature, 
moisture, or age. The ideal fixed 
resistor for B-eliminator hookups. 

i The BRADLEYOHM-E 



is standard 



I 





equipment 
for accu- 
rate plate 
voltage 
control on 
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ing B-elim- 
inators. 
Scientifi- 
cally-treated discs in the Bradley- 
ohm-E provide noiseless, stepless 
plate voltage control. 

The BRADLEYLEAK 

A vari- 
able grid 
leak that 
provides 
perfect 
grid leak 
adjust' 
m e n t , 
thereby 
provid- 
ing the 
best possible results with any tube. 

The BRADLEYSTAT 

The ideal 
f i lament 
control. 
Gives noise- 
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control for 
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Can be easi- 
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When you build a set or B-elimina- 
tor, demand Allen -Bradley Perfect 
Radio Resistors to secure best results 



Electric Controlling Apparatus 

27SGr D (i e ldAve. [fvD | Milwaukee. Wii 





A Varied List of Books Pertaining to Radio and Allied 
Subjects Obtainable Free With the Accompanying Coupon 



ID EADERS may obtain any of the booklets listed below by use* 
*^- ing tbe coupon printed on page 168. Order by number only. 



1. FILAMENT CONTROL Problems of filament supply, 
voltage regulation, and effect on various circuits. RADIALL 
COMPANY. 

2. HARD RUBBER PANELS Characteristics and proper- 
ties of hard rubber as used in radio, with suggestions on 
how to "work" it. B. F. GOODRICH RUBBER COMPANY. 

3. TRANSFORMERS A booklet giving data on input and 
output transformers. PACENT ELECTRIC COMPANY. 

4. RESISTANCE-COUPLED AMPLIFIERS A general dis- 
cussion of resistance coupling with curves and circuit dia- 
grams. COLE RADIO MANUFACTURING COMPANY. 

5. CARBORUNDUM IN RADIO A book giving pertinent 
data on the crystal as used for detection, with hook-ups, 
and a section giving information on the use of resistors. 
THE CARBORUNDUM COMPANY. 

6. B-ELIMINATOR CONSTRUCTION Constructional data 
on how to build. AMERICAN ELECTRIC COMPANY. 

7. TRANSFORMER AND CHOKE-COUPLED AMPLIFICA- 
TION Circuit diagrams and discussion. ALL-AMERICAN 
RADIO CORPORATION. 

8. RESISTANCE UNITS A data sheet of resistance units 
and their application. WARD-LEONARD ELECTRIC COMPANY. 

9. VOLUME CONTROL A leaflet showing circuits for 
distortionless control of volume. CENTRAL RADIO LABORA- 
TORIES. 

10. VARIABLE RESISTANCE As used in various circuits. 
CENTRAL RADIO LABORATORIES. 

1 1. RESISTANCE COUPLING Resistors and their ap- 
plication to audio amplification, with circuit diagrams. 
UBJUR PRODUCTS COMPANY. 

12. DISTORTION AND WHAT CAUSES IT Hook-ups of 
resistance-coupled amplifiers with standard circuits. ALLEN- 
BRADLEY COMPANY. 

1 5. B-ELIMINATOR AND POWER AMPLIFIER Instruc- 
tions for assembly and operation using Raytheon tube. 
GENERAL RADIO COMPANY. 

153. B-ELIMINATOR AND POWER AMPLIFIER Instruc- 
tions for assembly and operation using an R. C. A. rectifier. 
GENERAL RADIO COMPANY. 

16. VARIABLE CONDENSERS -A description of the func- 
tions and characteristics of variable condensers with curves 
and specifications for their application to complete receivers. 
ALLEN D. CARDWELL MANUFACTURING COMPANY. 

17. BAKEUTE A description of various uses of bakelite 
in radio, its manufacture, and its properties. BAKELITE 
CORPORATION. 

19. POWER SUPPLY A discussion on power supply with 
particular reference to lamp-socket operation. Theory 
and constructional data for building power supply devices. 
ACME APPARATUS COMPANY. 

20. AUDIO AMPLIFICATION A booklet containing data 
on audio amplification together with hints for the construc- 
tor. ALL AMERICAN RADIO CORPORATION. 

21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE- 
METER Constructional data and application. BURGESS 
BATTERY COMPANY. 

46. AUDIO-FREQUENCY CHOKES A pamphlet showing 

Eoshions in the circuit where audio- frequency chokes may 
e used. SAMSON ELECTRIC COMPANY. 

47. RADIO-FREQUENCY CHOKES Circuit diagrams il- 
lustrating the use of chokes to keep out radio- frequency 
currents from definite points. SAMSON ELECTRIC COMPANY. 

48. TRANSFORMER AND IMPEDANCE DATA Tables giving 
the mechanical and electrical characteristics of transformers 
and impedances, together with a short description of their 
use in the circuit. SAMSON ELECTRIC COMPANY. 

49. BYPASS CONDENSERS A description of the manu- 
facture of bypass and filter condensers. LESLIE F. MUTER 
COMPANY. 

50. AUDIO MANUAL Fifty questions which are often 
asked regarding audio amplification, and their answers. 
AMERTRAN SALES COMPANY, INCORPORATED. 

51. SHORT-WAVE RECEIVER Constructional data on a 
receiver which, -by the substitution of various coils, may be 
made to tune from a frequency of 16,660 kc. (18 meters) to 
1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED. 

52. AUDIO QUALITY A booklet dealing with audio-fre- 
quency amplification of various kinds and the application 
to well-known circuits. SILVER-MARSHALL. INCORPORATED. 

56. VARIABLE CONDENSERS A bulletin giving an 
analysis of various condensers together with their charac- 
teristics. GENERAL RADIO COMPANY. 

57. FILTER DATA Facts about the filtering of direct 
current supplied by means of motor-generator outfits used 
with transmitters. ELECTRIC SPECIALTY COMPANY. 

59. RESISTANCE COUPLING A booklet giving some 
general information on the subject of radio and the applica- 
tion of resistors to a circuit. DAVEN RADIO CORPORATION. 

60. RESISTORS A pamphlet giving some technical data 
on resistors which are capable of dissipating considerable 
energy; also data on the ordinary resistors used in resistance- 
coupled amplification. THE CRESCENT RADIO SUPPLY 
COMPANY. 

62. RADIO-FREQUENCY AMPLIFICATION Constructional 
details of a five-tube receiver using a special design of radio- 
frequency transformer. CAMFIELD RADIO MFG. COMPANY. 

63. FIVE-TUBE RECEIVER Constructional data on 
building a receiver. AERO PRODUCTS, INCORPORATED. 

64. AMPLIFICATION WITHOUT DISTORTION Data and 
curves illustrating the use of various methods of amplifica- 
tion. ACME APPARATUS COMPANY. 

66. SUPER-HETERODYNE Constructional details of a 
seven-tube set. G. C. EVANS COMPANY. 

70. IMPROVING THE AUDIO AMPLIFIER Data on the 
characteristics of audio transformers, with a circuit diagram 
showing where chokes, resistors, and condensers can be used. 
AMERICAN TRANSFORMER COMPANY. 

72. PLATE SUPPLY SYSTEM A wiring diagram and lay- 
out plan for a plate supply system to be used with a power 
amplifier. Complete directions for wiring are given. AMER- 
TRAN SALES COMPANY. 



80. FIVE-TUBE RECEIVER Data are given for the con- 
struction of a five-tube tuned radio-frequency receiver. 
Complete instructions, list of parts, circuit diagram, and 
template are given. ALL-AMERICAN RADIO CORPORATION. 

81. BETTER TUNING A booklet giving much general in- 
formation on the subject of radio reception with specific il- 
lustrations. Primarily for the non-technical home construc- 
tor. BREMER-TULLY MANUFACTURING COMPANY. 

, 82. SIX-TUBE RECEIVER A booklet containing photo- 
graphs, instructions, and diagrams for building a six-tube 
shielded receiver. SILVER-MARSHALL, INCORPORATED. 

83. SOCKET POWER DEVICE A list of parts, diagrams, 
and templates for the construction and assembly of socket 
power devices. JEFFERSON ELECTRIC MANUFACTURING COM- 
PANY. 

84. FIVE-TUBE EQUAMATIC Panel layout, circuit dia- 
grams, and instructions for building a five-tube receiver, to- 
gether with data on the operation of tuned radio-frequency 
transformers of special design. KARAS ELECTRIC COMPANY. 

85. FILTER Data on a high-capacity electrolytic con- 
denser used in filter circuits in connection with A socket 
power supply units, are given in a pamphlet. THE ABOX 
COMPANY. 

86. SHORT-WAVE RECEIVER A booklet containing data 
on a short-wave receiver as constructed for experimental 
purposes. THE ALLEN D. CARDWELL MANUFACTURING 
CORPORATION. 

88. SUPER-HETERODYNE CONSTRUCTION A booklet giv- 
ing full instructions, together with a blueprint and necessary 
data, for building an eight-tube receiver. THE GEORGE W. 
WALKER COMPANY. 

89. SHORT-WAVE TRANSMITTER Data and blue prints 
are given on the construction of a short-wave transmitter, 
together with operating instructions, methods of keying, and 
other pertinent data. RADIO ENGINEERING LABORATORIES. 

oo. IMPEDANCE AMPLIFICATION The theory and practice 
of a special type of dual-impedance audio amplification are 
given. ALDEN MANUFACTURING COMPANY. 

93. B-SOCKET POWER A booklet giving constructional 
details of a socket-power device using either the BH or 313 
type rectifier. NATIONAL COMPANY, INCORPORATED. 

94 POWER AMPLIFIER Constructional data and wiring 
diagrams of a power amplifier combined with a B-supply 
unit are given. NATIONAL COMPANY, INCORPORATED. 

ipo. A, B, AND C SOCKET-POWER SUPPLY A booklet 
giving data on the construction and operation of a socket- 
power supply using the new high-current rectifier tube. 
THE Q. R. S. Music COMPANY. 

101. USING CHOKES A folder with circuit diagrams of 
the more popular circuits showing where choke coils may 
be placed to produce better results. SAMSON ELECTRIC 
COMPANY. 

ACCESSORIES 

22. A PRIMER OF ELECTRICITY Fundamentals of 
electricity with special reference to the application of dry 
cells to radio and other uses. Constructional data on buzzers, 
automatic switches, alarms, etc. NATIONAL CARBON COM- 
PANY. 

23. AUTOMATIC RELAY CONNECTIONS A data sheet 
showing how a relay may be used to control A and B cir- 
cuits. YAXLEY MANUFACTURING COMPANY. 

25. ELECTROLYTIC RECTIFIER Technical data on a new 
type of rectifier with operating curves. KODEL RADIO 
CORPORATION. 

26. DRY CELLS FOR TRANSMITTERS Actual tests 
given, well illustrated with curves showing exactly what 
may be expected of this type of B power. BURGESS BATTERY 
COMPANY. 

27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS- 
MITTERS Characteristic curves and data on discharge tests. 
BURGESS BATTERY COMPANY. 

28. B BATTERY LIFE Battery life curves with general 
curves on tube characteristics. BURGESS BATTERY COM- 
PANY. 

29. How TO MAKE YOUR SET WORK BETTER A non- 
technical discussion of general radio subjects with hints on 
how reception may be bettered by using the right tubes. 
UNITED RADIO AND ELECTRIC CORPORATION. 

30. TUBE CHARACTERISTICS A data sheet giving con- 
stants of tubes. C. E. MANUFACTURING COMPANY. 

31. FUNCTIONS OF THE LOUD SPEAKER A short, non- 
technical general article on loud speakers. AMPLION COR- 
PORATION OF AMERICA. 

32. METERS FOR RADIO A catalogue of meters used in 
radio, with connecting diagrams. BURTON-ROGERS COM- 
PANY. 

33. SWITCHBOARD AND PORTABLE METERS A booklet 
giving dimensions, specifications, and shunts used with 
various meters. BURTON-ROGERS COMPANY. 

34. COST OF B BATTERIES An interesting discussion 
of the relative merits of various sources of B supply, HART- 
FORD BATTERY MANUFACTURING COMPANY. 

35. STORAGE BATTERY OPERATION An illustrated 
booklet on the care and operation of the storage battery. 
GENERAL LEAD BATTERIES COMPANY. 

36. CHARGING A AND B BATTERIES Various ways of 
connecting up batteries for charging purposes. WESTING- 
HOUSE UNION BATTERY COMPANY. 

37. CHOOSING THE RIGHT RADIO BATTERY Advice on 
what dry cell battery to use; their application to radio, 
with wiring diagrams. NATIONAL CARBON COMPANY. 

53. TUBE REACTIVATOR Information on the care of 
vacuum tubes, with notes on how and when they should be 
reactivated. THE STERLING MANUFACTURING COMPANY. 

54. ARRESTERS Mechanical details and principles of the 
vacuum type of arrester. NATIONAL ELECTRIC SPECIALTY 
COMPANY. 

55. CAPACITY CONNECTOR Description of a new device 
for connecting up the various parts of a receiving set, and 
at the same time providing bypass condensers between the 
leads. KUR/-KASCH COMPANY. 

(Continued on page 168) 



RADIO BROADCAST ADVERTISER 



153 



Vital Factors 

in attaining 

High Quality Reproduction 




High quality reproduction depends upon three things: 
correctly designed coupling units, proper use of ampli- 
fier tubes, and an efficient reproducing device. 

For over a decade the subject of audio frequency 
amplification has been extensively studied in the labora- 
tories of the General Radio Company with particular 
attention given to the design of coupling units. 

As a result of this exhaustive research the General 
Radio Company has been, and is, the pioneer manufac- 
turer of high quality Audio Transformers, Impedance 
Couplers, and Speaker Filters. 

The latest contribution to quality amplification is the 
type 441 Push-Pull Amplifier, which is mounted on a 
The Type 285 transformers give high nickel finished metal base-board and is completely wired. 

and even amplification of a!) tones * 

If the amplifier of your receiver is not bringing out 
the rich bass notes and the mellow high tones as well as 
those in the middle register why not rebuild your ampli- 
fier for Quality Reproduction with General Radio coupling 




Type 285 
Audio Transformer 



common to speech, instrumental, and 
vocal music. Available in two ratios. 
Type 285-H Audio Transformer. 

Price $6.00 
Type 285-D Audio Transformer. 

Price $6.00 

Type 367 
Output Transformer 

This unit adapts the impedance of 
an audio amplifier to the input of any 
cone type speaker, thus promoting 
better tone quality and protecting the 
speaker windings against possible dam- 
age from A. C. voltages. Similar in 
appearance to the Type 285. 
Type 367 Output Transformer. 

Price $5.00 



units r 



Write for our Series A of amplification booklets de- 
scribing various amplifier circuits and units. 

GENERAL RADIO COMPANY 

Cambridge, Mass. 



Type 373 

Double Impedance 
Coupler 

Many prefer the impedance coupling 
method of amplification to resistance 
coupling as lower plate voltages may 
be used and greater amplification may 
be obtained. The Type 373 is con- 
tained in a meta! shell and connected 
in a circuit in precisely the same man- 
ner as a transformer. 
Type 373 Double Impedance Coupler. 
Price $6.50 

Type 387 -A 
Speaker Filter 

The Type 387-A consists of an in- 
ductance choke with condenser. It 
offers a high impedance to audio fre- 
quency current and forces these cur- 
rents to pass through a condenser into 
the speaker, thereby improving tone 
quality and protecting the speaker 
windings. 
Type 387-A Speaker Filter. 

Price $6.00 




Type 441 Push-Pull Amplifier 

The Type 441 is completely wired and consists of two high quality push-pull trans- 
formers, with necessary sockets and resistances mounted on a nickel finished metal 
base board. It may be used with any power or semi-power tube to increase the un- 
distorted output of the amplifier with the result that better quality is reproduced from 
the loudspeaker with more volume than is obtained from other methods of coupling. 

Licensed by the R. C. A. and through terms of the license may be sold with tubes only. 

Type 441 Push-Pull Amplifier Price $20.00 

Type UX-226 or CX-326 Amplifier Tube 3.00 

Type UX-I7I or CX-37I Amplifier Tube " 4.50 




Type 445 Plate Supply and Grid Biasing Unit 

1 he Type 445 meets the demand for a thoroughly dependable light socket plate 
supply and grid biasing unit that is readily adaptable to the tube requirements of any 
standard type of receiver. Any combination of voltages from o to 100 may be taken 
from the adjustable "B" voltage taps. A variable grid bias voltage from o to 50 is 
also available. The unit is designed for use on 105 to 125 volt (50 to 60 cycle) A. C. 
lines and uses the UX-28O or CX-3KO rectifier tube. 

Licensed by R. C. A. and through terms of the license may be sold with tube only. 

Type 445 Plate Supply and Grid Biasing Unit Price $55.00 

Type UX-;8o or CX-38o Rectifier Tube " 5.00 





ENERAl 

LABORATORY EQUIPMENT 

Parts and Accessories 



154 



RADIO BROADCAST ADVERTISER 



"RADIO BROADCASTS" DIRECTORY OF 
MANUFACTURED RECEIVERS 



<J A coupon will be found on page 172. All readers who desire additional 
information on the receivers listed below need only insert the proper num- 



bers in the coupon, mail it to the Service Department of RADIO BROADCAST, 
and full details will be sent. New sets are listed in this space each month. 



KEY TO TUBE ABBREVIATIONS 

99 60-mA. filament (dry cell) 

01 -A Storage battery 0.25 amps, filament 

12 Power tube (Storage battery) 

71 Power tube (Storage battery) 

16-B Half-wave rectifier tube 

80 Full-wave, high current rectifier 

81 Half-wave, high current rectifier 

Hmu High-Mu tube for resistance-coupled audio 

20 Power tube (dry cell) 

10 Power Tube (Storage battery) 

00-A Special detector 

13 Full-wave rectifier tube 

26 Low-voltage high-current a. c. tube 

27 Heater type a. c. tube 



DIRECT CURRENT RECEIVERS 
NO. 424. COLONIAL 26 

Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans- 
former audio (01-A and 71). Balanced t. r. f. One to 
three dials. Volume control: antenna switch and poten- 
tiometer across first audio. Watts required: 120. Con- 
sole size: 34 x 38 x 18 inches. Headphone connections. 
The filaments are connected in a series parallel arrange- 
ment. Price $250 including power unit. 

NO. 425. SUPERPOWER 

Five tubes: All 01-A tubes. Multiplex circuit. Two 
dials. Volume control: resistance in r. f. plate. Watts 
required: 30. Antenna: loop or outside. Cabinet sizes: 
table, 27 x 10 x 9 inches; console, 28 x 50 x 21. Prices: 
table, $135 including power unit; console, $390 includ- 
ing power unit and loud speaker. 

A. C. OPERATED RECEIVERS 

NO. 508. ALL-AMERICAN 77, 88, AND 99 

Six tubes; 3 t. r. f. (26), detector (27), 2 transformer 
audio (26 and 71). Rice neutralized t. r. f. Single drum 
tuning. Volume control: potentiometer in r. f. plate. 
Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy, 
25 x 38 x 18 inches; No. 99 console,'27j x 43 x 20 inches. 
Shielded. Output device. The filaments are supplied 
by means of three small transformers. The plate supply 
employs a gas-filled rectifier tube. Voltmeter in a. c. 
supply line. Prices: No. 77, $150, including power unit; 
No. 88, $210 including power unit; No. 99, $285 in- 
cluding power unit and loud speaker. 

NO. 509. ALL-AMERICAN "DUET"; "SEXTET" 

Six tubes; 2 t. r. f. (99), detector (99), 3 transformer 
audio (99 and 12). Rice neutralized t.r.f. Two dials. 
Volume control: resistance in r.f. plate. Cabinet sizes: 
"Duet," 23 x 56x16} inches; "Sextet," 22}x 13} x 15} 
inches. Shielded. Output device. The 99 filaments are 
connected in series and supplied with rectified a.c., 
while 12 is supplied with raw a.c. The plate and fila- 
ment supply uses gaseous rectifier tubes. Milliammeter 
on power unit. Prices: "Duet," $160 including power 
unit; "Sextet," $220 including power unit and loud 
speaker. 

NO. 511. ALL-AMERICAN 80, 90, AND 115 

Five tubes; 2 t.r.f. (99). detector (99), 2 transformer 
audio (99 and 12). Rice neutralized t.r.f. Two dials. 
Volume control: resistance in r.f. plate. Cabinet sizes: 
No. 80, 231 x 12} x 15 inches; No. 90, 37} x 12 x 12} 
inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi- 
vidually shielded. Output device. See No. 509 for 
power supply. Prices: No. 80, $135 including power 
unit; No. 90, $145 including power unit and compart- 
ment; No. 115, $170 including power unit, compart- 
ment, and loud speaker. 

NO. 510. ALL-AMERICAN 7 

Seven tubes; 3 t.r.f. (26). 1 untuned r.f. (26), detector 
(27), 2 transformer audio (26 and 71). Rice neutralized 
t.r.f. One drum. Volume control: resistance in r.f. 
plate. Cabinet sizes: "Sovereign" console, 30} x 60} 
x 19 inches; "Lorraine" Hiboy, 25} x 53j x 17J inches; 
"Forte" cabinet, 25} x 13} x 17} inches. For filament 
and plate supply: See No. 508. Prices: "Sovereign" 
$460; "Lorraine" $360; "Forte" $270. All prices include 
power unit. First two include loud speaker. 

NO. 401. AMRAD AC9 

Six tubes; 3 t.r.f. (99), detector (99), 2 transformer 
(99 and 12). Neutrodyne. Two dials. Volume control: 
resistance across 1st audio. Watts consumed: 50. Cabi- 
net size: 27 x 9 x 11J inches. The 99 filaments are con- 
nected in series and supplied with rectified a.c., while 
the 12 is run on raw a.c. The power unit, requiring two 
16-B rectifiers, is separate and supplies A, B, and C 
current. Price $142 including power unit. 

NO. 402. AMRAD ACS 

Five tubes. Same as No. 401 except one less r.f. 
stage. Price $125 including power unit. 

NO. 536. SOUTH BEND 

Six tubes. One control. Sub-panel shielding. Binding 
Posts. Antenna: outdoor. Prices: table, $130, Baby 
Grand console, $195. 

NO. 537. WALBERT 26 

Six tubes; five Kellogg a.c. tubes and one 71. Two 
controls. Volume control: variable plate resistance. 
Isofarad circuit. Output device. Battery cable. Semi- 
shielded. Antenna: 50 to 75 feet. Cabinet size: 10} x 
SH x 16J inches. Prices: $215; with tubes, $250. 



NO. 484. BOSWORTH, B5 

Five tubes; 2 t.r.f. (26), detector (99), 2 transformer 
audio (special a.c. tubes). T.r.f. circuit. Two dials^ 
Volume control: potentiometer. Cabinet size: 23 x 7 
x 8 inches. Output device included. Price $175. 

NO. 406. CLEARTONE 110 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All tubes a. c. heater type. One or two dials. Volume 
control: resistance in r. f. plate. Watts consumed: 40. 
Cabinet size- varies. The plate supply is built in the 
receiver and requires one rectifier tube. Filament sup- 
ply through step down transformers. Prices range from 
$175 to $375 which includes 5 a.c. tubes and one rectifier 
tube. 

NO. 407. COLONIAL 25 

Six tubes; 2 t. r. f. (01-A), detector (99), 2 resistance 
audio (99). 1 transformer audio (10). Balanced t.r.f. 
circuit. One or three dials. Volume control: Antenna 
switch and potentiometer on 1st audio. Watts con- 
sumed: 100. Console size: 34 x 38 x 18 inches. Output 
device. All tube filaments are operated on a. c. except 
the detector which is supplied with rectified a.c. from 
the plate supply. The rectifier employs two 16-B tubes. 
Price $250 including built-in plate and filament supply. 

NO. 507. CROSLEY 602 BANDBOX 

Six tubes; 3 t.r.f. (26), detector (27), 2 transformer 
audio (26 and 71). Neutrodyne circuit. One dial, 
Cabinet size: 17J x 5} x 7| inches. The heaters for the 
a.c. tubes and the 71 filament are supplied by windings in 
B unit transformers available to operate either on 25 or 
60 cycles. The plate current is supplied by means of 
rectifier tube. Price $65 for set alone, power unit $60. 

NO. 408. DAY-FAN "DE LUXE" 

Six tubes; 3 t.r.f., detector, 2 transformer audio. All 
01-A tubes. One dial. Volume control: potentiometer 
across r.f. tubes. Watts consumed: 300. Console size: 
30 x 40 x 20 inches. The filaments are connected in 
series and supplied with d.c. from a motor-generator 
set which also supplies B and C current. Output de- 
vice. Price $350 including power unit. 

NO. 409. DAYCRAFT 5 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All a. c. heater tubes. Reflexed t.r.f. One dial. Volume 
control: potentiometers in r.f. plate and 1st audio. 
Watts consumed: 135. Console size: 34 x 36 x 14 inches. 
Output device. The heaters are supplied by means of 
a small transformer. A built-in rectifier supplies B 
and C voltaces. Price $170, less tubes. The following 
have one more r.f. stage and are not reflexed: Day- 
craft 6, $195; Dayrole 6, $235; Dayfan 6, $110. All 
prices less tubes. 

NO. 469. FREED-EISEMANN NR11 

Six tubes; 3 t.r.f. (01-A). detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. One dial. 
Volume control: potentiometer. Watts consumed: 150. 
Cabinet size: 19} x 10 x 10} inches. Shielded. Output 
device. A special power unit is included employing a 
rectifier tube. Price $225 including NR-411 power unit. 

NO. 487. FRESHMAN 7F-AC 

Six tubes; 3 t.r.f. (26), detector (27), 2 transformer 
audio (26 and 71). Equaphase circuit. One dial. Volume 
control: potentiometer across 1st audio. Console size: 
24} x 41} x 15 inches. Output device. The filaments and 
heaters and B supply are all supplied by one power unit. 
The plate supply requires one 80 rectifier tube. Price 
$175 to $350, complete. 

NO. 421. SOVEREIGN 238 

Seven tubes of the a.c. heater type. Balanced t.r.f. 
Two dials. Volume control: resistance across 2nd audio. 
Watts consumed: 45. Console size: 37 x 52 x 15 inches. 
The heaters are supplied by a small a. c. transformer. 
while the plate is supplied by means of rectified a.c 
using a gaseous type rectifier. Price $325, including 
power unit and tubes. 

NO. 517. KELLOGG 510, 511, AND 512 

Seven tubes; 4 t.r.f., detector, 2 transformer audio. 
All Kellogg a.c. tubes. One control and special zone 
switch. Balanced. Volume control: special. Output de- 
vice. Shielded. Cable connection between power supply 
unit and receiver. Antenna: 25 to 100 feet. Panel "1$ 
x 27} inches. Prices: Model 510 and 512, consoles, $495 
complete. Model 511, consolette, $365 without loud 
speaker. 

NO. 496. SLEEPER ELECTRIC 

Five tubes; four 99 tubes and one 71. Two controls. 
Volume control: rheostat on r.f. Neutralized. Cable. 
Output device. Power supply uses two 16-B tubes. 
Antenna: 100 feet. Prices: Type 64, table. $160; Type 
65, table, with built-in loud speaker, $175; Type 66, 
table, $175; Type 67, console, $235; Type 78, console, 
$265. 

NO. 538. NEUTROWOUND, MASTER ALLECTRIC 

Six tubes; 2 t.r.f. (01-A), detector (pl-A), 2 audio 
(01-A and two 71 in push-pull amplifier). The 01-A 
tubes are in series, and are supplied from a 400-mA. 
rectifier. Two drum controls. Volume control: variable 
plate resistance. Output device. Shielded. Antenna: 
50 to 100 feet. Price: S!60. 



NO. 413. MARTI 

Six tubes: 2 t.r.f., detector, 3 resistance audio. All 
tubes a.c. heater type. Two dials. Volume control' 
resistance in r.f. plate. Watts consumed: 38. Panel size 
7 x 21 inches. The built-in plate supply employs one 
16-B rectifier. The filaments are supplied by a small 
transformer. Prices: table, $235 including tubes and 
rectifier; console, $275 including tubes and rectifier; 
console, $325 including tubes, rectifier, and loud speaker. 

NO. 417 RADIOLA 28 

Eight tubes; five type 99 and one type 20. Drum 
control. Super-heterodyne circuit. C-battery connec- 
tions. Battery cable. Headphone connection. Antenna: 
loop. Set may be operated from batteries or from the 
power mains when used in conjunction with the model 
104 loud speaker. Prices: $260 with tubes, battery 
operation; $570 with model 104 loud speaker, a. c. 
operation. 

NO. 540 RADIOLA 30-A 

Receiver characteristics same as No. 417 except that 
type 71 power tube is used. This model is designed to 
operate on either a. c. or d. c. from the power mains. 
The combination rectifier power amplifier unit uses 
two type 81 tubes. Model 100-A loud speaker is con- 
tained in lower part of cabinet. Either a short indoor 
or long outside antenna may be used. Cabinet size: 
42Vi x 29 x 17% inches. Price: $495. 

NO. 541 RADIOLA 32 

This model combines receiver No. 417 with the model 
104 loud speaker. The power unit uses two type 81 
tubes and a type 10 power amplifier. Loop is completely 
enclosed and is revolved by means of a dial on the panel. 
Models for operation from a. c. or d. c. power mains. 
Cabinet size: 52 x 72 x 17% inches. Price: $895. 

NO. 539 RADIOLA 17 

Six tubes; 3 t. r. f. (26), detector (27), 2 transformer 
audio (26 and 27). One control. Illuminated dial. 
Built-in power supply using type 80 rectifier. Antenna: 
100 feet. Cabinet size: 25,", x 7% x 8'/ 8 . Price: $130 
without accessories. 

NO. 545. NEUTROWOUND, SUPER ALLECTRIC 

Five tubes; 2 t.r.f. (99), detector (99). 2 audio (99 
and 71). The 99 tubes are in series and are supplied from 
an 85-mA. rectifier. Two drum controls. Volume con- 
trol: variable plate resistance. Output device. Antenna: 
75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price: 
$150. 

NO. 490. MOHAWK 

Six tubes; 2 t.r.f., detector, 2 transformer audio. All 
tubes a.c heater type except 71 in last stage. One dial. 
Volume control: rheostat on r.f. Watts consumed: 40. 
Panel size: 12} x 8| inches. Output device. The heaters 
for the a.c tubes and the 71 filament are supplied by 
small transformers. The plate supply is of the built-in 
type using a rectifier tube. Prices range from $65 to 
$245. 

NO. 522. CASE, 62 B AND 62 C 

McCullough a.c. tubes. Drum control. Volume con- 
trol; variable high resistance in audio system. C-battery 
connections. Semi-shielded. Cable. Antenna: 100 feet. 
Panel size: 7 x 21 inches. Prices: Model 62 B, complete 
with a.c. equipment, $185; Model 62 C, complete with 
a.c. equipment, $235. 

NO. 523. CASE, 92 A AND 92 C 

McCullough a.c. tubes. Drum control. Inductive 
volume control. Technidyne circuit. Shielded. Cable. 
C-battery connections. Model 92 C contains output 
device. Loop operated. Prices: Model 92 A, table, $350; 
Model 92 C, console, $475. 



BATTERY OPERATED RECEIVERS 



NO. 542. PFANSTIEHL JUNIOR SIX 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio. 
Pfanstiehl circuit. Volume control: variable resistance in 
r.f. plate circuit. One dial. Shielded. Battery cubic. C- 
battery connections. Etched bronze panel. Antenna : out- 
door. Cabinet size: 9 x 2O x 8 inches. Price: $80, without 
accessories. 

NO. 512. ALL-AMERICAN 44, 45, AND 66 

Six tubes; 3 t.r.f. (01-A, detector) 01 -A, 2 transformer 
audio (01-A and 71). Rice neutralized t.r.f. Drum 
control. Volume control: rheostat in r.f. Cabinet sizes: 
No. 44, 21 x 10 x 8 inches; No. 55. 25 x 38 x 18 inches; 
No. 66, 27J x 43 x 20 inches. C-battery connections. 
Battery cable. Anienna: 75 to 125 feet. Prices: No. 44, 
$70; No. 55, $125 including lud speaker; No. 66, $200 
including loud speaker. 

NO. 428. AMERICAN C6 

Five tubes; 2 t.r.f, detector, 2 transformer audio. 
All 01-A tubes. Semi balanced t.r.f. Tnrce dials. Plate 
current 15 mA. Volume control: potentiometer. Cabinet 
sizes: table, 20 x 8} x 10 inches; console. 36 x 40 x 17 
inches. Partially shielded. Battery cable. C-batler> 
connections. Antenna: 125 feet. Prices: table, $30 
console. $(if> including loud speaker. 



RADIO BROADCAST ADVERTISER 



155 



ALL 
METAL 

SHIELDED 
SIS 




MAGNIFICENT TONE- SUPER SELECTIVE-POWERFUL DISTANCE GETTER \ 




or Battery Set.' 



t 



Risers Say: 



Reports from us era everywhere 
leave little fur us to add. These are 
only a few of the many in our files 
and which we receive daily. Se 



. 
TRICO MANY SETS-MIRACO BEST 

Miraco is best set I've ever heard. 
It's just the set I've always wanted 
and I've had so many setslgot justa 
little hard-boiled about believing 
there were any sets perfect. I sure 
got ray wish. I've had just 104 sta- 
tions. There's about a station to 
each number on dial. I get KFI 
(Cal.) every night. Had PWX last 
night and got 6KAV tonight good 
and loud. FRANCIS ARM- 
BRUSTER. Cleveland, Ohio. 
P.is. Youpackyoursetswonderful. 

HE KNOWS SETS-READ THIS 
I have built radios since they first 
made their appearance and it has 
been my pleasure to build, repair 
and self them. For quality, selec- 
tivity and sensitivity it is my firm 
belief that the Miraco cannot be 
excelled. I have proven beyond any 
shadow of doubt that it will out- 
perform any other radios. I bring in 
the farthest distance with little or 
no effort. TheMiracoalsogivesme 
tone quality. URBAIN BARIL, 
Jr., Fall River, Mass. 
MIRACO EXCELS EXPENSIVE RADIOS 
The Miraco set and loud speaker 
beat anything around here, regard- 
less of price. Have tried them out 
against a $200 outfit. Have logged 
140 stations, coast tocoast. E. J. 
CARR1FRE, Bathgate, N. D. 

HEARS CUBA, CANADA. MEXICO 
Afriend visited here that has close to 
S300in a radio but no better tone 
and no plainer than the Miraco. 
Have gotten 



America's big, old, reliable Ra- 
dio Corporation* (8th successful 
year) guarantees in its big:, 
powerful, latest 6, 7 and 8 tube 
Miraco Beta "the finest, most 
enjoyable performance obtain- 
able in high grade radios." 
Unless 30 days' use in your 
homef ully satisfies you a Miraco 
is unbeatable at any price for 
beautiful, clear cathedral tone, 
razor-edge selectivity, power- 
ful distance recpption, easy 
operation, etc. don't buy it! 
Your verdict final. Save or 
make lots of money on Bets and 
equipment" write for testimony 
01 nearby users and Amazing 
Special Factory Offer. 

Miraco's work equally fine 
on "AC" electric house 
current or with batteries. 

Take your choice. Many thou- 
sands of Miraco users who 
bought after thorough com- 
parisonsenjoy programs Coast 




to Coast, Canada to Mexico, 
loud and cleat with the mag- 
nificent cathedral tone quality 
of costliest seta. Don't con- 
fuse Miraco's with cheap, 
"squawky" radios. Miraco's 
have finest parts, latest ap- 
proved shielding, metal chassis, 
etc. as used in many $200 sets. 

Deal Direct 
with Big Factory 

Your Miraco reaches you com- 
pletely assembled, rigidly test- 
ed, fully guaranteed. Easy to 
connect and operate. 3O days' 
trial free. S year guarantee if 
you buy. You take no risk, you 
insure satisfaction, you enjoy 
rock -bottom money -sav- 
ing prices by dealing direct 
with one of radio's oldest, most 
successful builders of fine sets. 
8th successful year in the radio 
manufacturing business. 

USER-AGENTS! Make bis profits showing Mlraca 

to friends. Get Our Special Wholesale Prices! 
MIDWEST RADIO CORPORATION, Cincinnati, O. 

BEAUTIFULLY ILLUSTRATED CATALOG 
AND AMAZING 
SPECIAL OFFER 



SEND NO MONEY 30 
DAYS' TRIAL, Special 
sale Price Offer to User-Apents, Bank 
:es, testimony of nearby iairacou^crg 
proof you want sent with catalog:. 

mail coupon right now j 



f 




User-Agents 



one dial 

METAL SHIELDED 
CHASSIS 



MIRACO "Powerpluss" 

both in 8 and 7 tube models 

havr magnificently beautiful, 

clear cathedral tone quality. I urn 
one dial for stations everywhere. 
Ultra-t elective. Miraco multistage 
distance amplification gives "power* 
plus" on fir-oif stations. Latest 
all-metal shielded chassis. Illun.fn- 
ated dial. Fully guaranteed. Try 
one jrte far JO days I Choice ot 
beautiful cabinets. 



RETAIL LIST 



ElectrifyJVny Radio 
MIDWEsflNO-BATTERY 



BIG 
DISCOUNT 

TO 

User- Agent 



COUPON 

NOT 
ORDER 




outbatteries! WriteforMiciwertprlcee 
and discounts. Midwest Units are highest 

trade laatiDgly dependable. QUMt la o 

etioD, fully guaranteed. 



CUTS THRU NEW YORK LOCALS 

I can get distance thru the locals I 
when they are all on early i n the I 

evening. J. F.LOGAN, Rock- 
X away Beach. New York. 



Another Big Bargain! Famous pow- 
erful big Miraco Super 6, 1928 model- 
ultra selective ! Thousands find it out- 
performs sets of much higher price. 
3O Days' Trial Free. Fully 
Guaranteed. 



r MIDWEST RADIO CORPORATION 

Pioneer Builders ofSet$ 
406 K Miraco Building, Ou.cini.ati, Ohio. 

Without obligation, send free catalog, AMAZING SPECIAL OFFER, testimony of 
nearby Miraco users. D User Q Agent D Dealer 

NAME 



I ADDRESS 



1.56 



RADIO BROADCAST ADVERTISER 



NO. 485. BOSWORTH B6 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Two dials. Volume control: 
variable grid resistances. Battery cable. C battery 
connections. Antenna: 25 feet or longer. Cabinet size 
15 x 7 x 8 inches. Price $75. 

NO. 513. COUNTERPHASE SIX 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 12). Counterphase t.r.f. Two 
dials. Plate current: 32 mA. Volume control: rheostat 
on 2nd and 3rd r.f. Coils shielded. Battery cable. C- 
battery connections. Antenna: 75 to 100 feet. Console 
size: 18f x 40} x 15j inches. Prices: Model 35, table, 
$110; Model 37, console, $175. 

NO. 514. COUNTERPHASE EIGHT 

Eight tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 12). Counterphase t.r.f. One 
dial. Plate current: 40 mA. Volume control: rheostat in 
1st r.f. Copper stage shielding. Battery cable. C-battery 
connections. Antenna: 75 to 100 feet. Cabinet size: 
30 x 12} x 16 inches. Prices: Model 12, table, $225; 
Model 16, console, $335; Model 18, console, $365. 

NO. 506. CROSLEY 601 BANDBOX 

Six tubes; 3 t.r.f., detector, 2 transformer audio. All 
01-A tubes. Neutrodyne. One dial. Plate current: 
40 mA. Volume control: rheostat in r.f. Shielded. 
Battery cable. C-battery connections. Antenna: 75 to 
150 feet. Cabinet size: 17J x 5} x 7|. Price, $55. 

NO. 434. DAY-FAN 6 

Six tubes: 3 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 12 or 71). One dial. Plate 
current: 12 to 15 mA. Volume control: rheostat on r.f. 
Shielded. Battery cable, C battery connections. Output 
device. Antenna: 50 to 120 feet. Cabinet sizes: Daycraft 
6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7. 
Prices: Day-Fan 6, $110; Daycraft 6, $145 including 
loud speaker; Day-Fan Jr. not available. 

NO. 435. DAY-FAN 7 

Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 resist- 
ance audio (01-A), 2 transformer audio (01-A and 12 
or 71). Plate current: 15 mA. Antenna: outside. Same 
as No. 434. Price $115. 

NO. 503. FADA SPECIAL 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. Two drum 
control. Plate current: 20 to 24 mA. Volume control: 
rheostat on r.f. Coils shielded. Battery cable. C-battery 
connections. Headphone connection. Antenna: outdoor. 
Cabinet size: 20} x 13J x 10i inches. Price $95. 

NO. 504. FADA 7 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. Two drum 
control. Plate current: 43mA. Volume control: rheostat 
on r.f. Completely shielded. Battery cable. C-battery 
connections. Headphone connections. Output device. 
Antenna: outdoor or loop. Cabinet sizes: table, 25} x 
13} x 11} inches; console, 29 x 50 x 17 inches. Prices: 
table, $185; console, $285. 

NO. 436. FEDERAL 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 12 or 71). Balanced t.r.f. One 
dial. Plate current: 20.7 mA. Volume control: rheostat 
on r.f. Shielded. Battery cable. C-battery connections. 
Antenna: loop. Made in 6 models. Price varies from 
$250 to $1000 including loop. 

NO. 505. FADA 8 

Eight tubes. Same as No. 504 except for one extra 
stage of audio and different cabinet. Prices; table, $300; 
console, $400. 

NO. 437. FERGUSON 10A 

Seven tubes; 3 t.r.f. (01-A), detector (01-A), 3 audio 
(01-A and 12 or 71). One dial. Plate current: 18 to 25 
mA. Volume control: rheostat on two r.f. Shielded. 
Battery cable. C-battery connections. Antenna: 100 
feet. Cabinet size: 21} x 12 x 15 inches. Price $150. 

NO. 438. FERGUSON 14 

Ten tubes; 3 untuned r.f., 3 t. r.f. (01-A), detector 
(01-A), 3 audio (01-A and 12 or 71). Special balanced 
t.r.f. One dial. Plate current: 30 to 35 mA. Volume con- 
trol: rheostat in three r.f. Shielded. Battery cable, C- 
battery connections. Antenna: loop. Cabinet size: 
24 x 12 x 16 inches. Price $235, including loop. 

NO. 439. FERGUSON 12 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 1 trans- 
former audio (01-A), 2 resistance audio (01-A and 12 
or 71). Two dials. Plate current: 18 to 25 mA. Volume 
control: rheostat on two r.f. Partially shielded. Battery 
cable. C-battery connections. Antenna: 100 feet. 
Cabinet size: 22( x 10 x 12 inches. Price $85. Consolette 
$145 including loud speaker. 

NO. 440. FREED EISEMANN NR-8 NR-9, AND 
NR-66 

Six tubes; 3 t.r... (01-A), detector (01-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. NR-8, two 
dials; others one dial. Plate current: 30 mA. Volume 
control: rheostat on r.f. NR-8 and 9; chassis type 
shielding^ NR-66, individual stage shielding. Battery 
cable. C-battery connections. Antenna: 100 feet. 
Cabinet sizes: NR-8 and 9, 19 j x 10 x 10} inches; NR-66 
20 x 10} x 12 inches. Prices: NR-8, $90; NR-9, $100; 
NR-66, $125. 

NO. 501. KING "CHEVALIER" 

Six tubes. Same as No. 500. Coils completely shielded. 
Panel size: 11 x 7 inches. Price, $210 including loud 
speaker. 



NO. 441. FREED EISEMANN NR 77 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 
transformer audio (01-A and 71). Neutrodyne. One 
dial. Plate current: 35 mA. Volume control: rheostat on 
r.f. Shielding. Battery cable. C-battery connections. 
Antenna: outside or loop. Cabinet size: 23 x 10} x 13 
inches. Price $175. 

NO. 442. FREED-EISEMANN 800 AND 850 

Eight tubes; 4 t.r.f. (01-A), detector (01-A), 1 trans- 
former (01-A), 1 parallel audio (01-A or 71). Neutro- 
dyne. One dial. Plate current: 35 mA. Volume control: 
rheostat on r.f. Shielded. Battery cable. C-battery 
connections. Output: two tubes in parallel or one power 
tube may be used. Antenna: outside or loop. Cabinet 
sizes: No. 800, 34 x 15J x 13J inches; No. 850, 36 x 65J x 
17}. Prices not available. 

NO. 444. GREBE MU-1 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- 
former audio (01-A and 12 or 71). Balanced t.r.f. One, 
two, or three dials (operate singly or together). Plate 
current: 30mA. Volume control: rheostat on r.f. Bi- 
nocular coils. Binding posts. C-battery connections. 
Antenna: 125 feet. Cabinet size: 22} x 9} x 13 inches. 
Prices range from $95 to $320. 

NO. 426. HOMER 

Seven tubes; 4 t.r.f. (01-A); detector (01-A or OOA); 
2 audio (01-A and 12 or 71). One knob tuning control. 
Volume control: rotor control in antenna circuit. Plate 
current: 22 io25mA. "Technidyne" circuit. Completely 
enclosed in aluminum box. Battery cable. C-battery con- 
nections. Cabinet size, 8| x 19} x 9i inches. Chassis size, 
6J x 17 x 8 inches. Prices: Chassis only, &80. Table cabi- 
net, $95. 

NO. 502. KENNEDY ROYAL 7. CONSOLETTE 

Seven tubes; 4 t.r.f. (01-A), detectx>r (00-A), 2 trans- 
former audio (01-A and 71). One dial. Plate current: 
42 mA. Volume control: rheostat on two r.f. Special 
r.f. coils. Battery cable. C-battery connections. Head- 
phone connection. Antenna: outside or loop. Consolette 
size: 36} x 35} x 19 inches. Price $220. 

NO. 498. KING "CRUSADER" 

Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans- 
former audio (01-A and 71). Balanced t.r.f. One dial. 
Plate current: 20 mA. Volume control: rheostat on r.f. 
Coils shielded. Battery cable. C-battery connections. 
Antenna: outside. Panel: 11 x 7 inches. Price, $115. 

NO. 499. KING "COMMANDER" 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). Balanced t.r.f. One dial. 
Plate current: 25 mA. Volume control: rheostat on r.f. 
Completely shielded. Battery cable. C-battery con- 
nections. Antenna: loop. Panel size: 12 x 8 inches. 
Price $220 including loop. 

NO. 429. KING COLE VII AND VIII 

Seven tubes; 3 t.r.f., detector, 1 resistance audio, 2 
transformer audio. All 01-A tubes. Model VIII has one 
more stage t.r.f. (eight tubes). Model VII, two dials. 
Model VIII, one dial. Plate current: 15 to 50 mA. 
Volume control: primary shunt in r.f. Steel shielding. 
Battery cable and binding posts. C-battery connections. 
Output devices on some consoles. Antenna: 10 to 100 
feet. Cabinet size: varies. Prices: Model VII, $80 to 
$160; Model VIII, $100 to $300. 

NO. 500. KING "BARONET" AND "VIKING" 

Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 trans- 
former audio (01-A and 71). Balanced t.r.f. One dial. 
Plate current: 19 mA. Volume control: rheostat in r.f. 
Battery cable. C-battery connections. Antenna: out- 
side. Panel size: 18x7 inches. Prices: "Baronet," $70; 
"Viking," $140 including loud speaker. 

NO. 489. MOHAWK 

Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio 
(01-A and 71). One dial. Plate current; 40 mA. Volume 
control: rheostat on r.f. Battery cable. C-battery con- 
nections. Output device. Antenna: 60 feet. Panel size: 
12} x 8J inches. Prices range from $65 to $245. 

NO. 543. ATWATER KENT, MODEL 33 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71 or 12). One dial. Volume control: r.f. fila- 
ment rheostat. C-battery connections. Battery cable. 
Antenna: 100 feet. Steel panel. Cabinet size: 21 ix6f x 61 
inches. Price: $75, without accessories. 

NO. 544. ATWATER KENT, MODEL 50 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 12 or 71 ). Volume control: r.f. filament rheo- 
stat. C-battery connections. Battery cable. Special band- 
pass filter circuit with an untuned amplifier. Cabinet 
size: 20J x 13 x 7J inches Price: $120. 

NO. 452. ORIOLE 90 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All 01-A tubes. "Trinum" circuit. Two dials. Plate 
current: 18 mA. Volume control: rheostat on r. f. 
Battery cable. C-battery connections. Antenna: 50 to 
100 feet. Cabinet size: 25} x 11} x 12} inches. Price 
$85. Another model has 8 tubes, one dial, and is 
shielded. Price $185. 

NO. 453. PARAGON 

Six tubes; 2 t.r.f. (01-A), detector (01-A). 3 double 
impedance audio (01-A and 71). One dial. Plate cur- 
rent: 40 mA. Volume control: resistance in r.f. plate. 
Shielded. Battery cable. C-battery connections. Out- 
put device. Antenna: 100 feet. Console size: 20 x 46 
x 17 inches. Price not determined. 



NO. 543 RADIOLA 20 

Five tubes; 2 t. r. f. (99), detector (99), two trans- 
former audio (99 and 20). Regenerative detector. Two 
drum controls. C-battery connections. Battery cable. 
Antenna: 100 feet. Price: $78 without accessories. 

NO. 480. PFANSTIEHL 30 AND 302 

Six tubes; 3 t.r.f. (01-A), detector (01- 2A), trans- 
former audio (01-A and 71). One dial. Plate current: 
23 to 32 mA. Volume control: resistance in r.f. plate. 
Shielded. Battery cable. C-battery connections. An- 
tenna: outside. Panel size: 172 x 8} inches. Prices: No. 
30 cabinet, $105; No. 302 console, $185 including 
loud speaker. 

NO. 515. BROWNING-DRAKE 7-A 

Seven tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio 
(Hmu, two 01-A, and 71). illuminated drum control. 
Volume control: rheostat on 1st r.f. Shielded. Neutral- 
ized. C-battery connections. Battery Cable. Metal 
panel. Output device. Antenna: 50-75 feet. Cabinet, 
30 x 11 x 9 inches. Price, $145. 

NO. 516. BROWNING-DRAKE 6-A 

Six tubes; 1 t.r.f. (99), detector (00-A), 3 audio 
(Hmu, two 01-A and 71). Drum control with auxiliary 
adjustment. Volume control : rheostat on r.f. Regenera- 
tive detector. Shielded. Neutralized. C-battery connec- 
tions. Battery cable. Antenna: 50-100 feet. Cabinet, 
25 x 11 x9. Price $105. 

NO. 518. KELLOGG "WAVE MASTER," 
504, 505, AND 506. 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
One control and special zone switch. Volume control: 
rheostat on r.f. C-battery connections. Binding posts. 
Plate current: 25 to 35 mA. Antenna: 100 feet. Panel: 
7} x 25} inches. Prices: Model 504, table, $75, less 
accessories. Model 505, table, $125 with loud speaker. 
Model 506, consolette, $135 with loud speaker. 

NO. 519. KELLOGG, 507 AND 508. 

Six tubes, 3 t.r.f., detector, 2 transformer audio. One 
control and special zone switch. Volume control : rheo- 
stat on r.f. C-battery connections. Balanced. Shielded. 
Binding posts and battery cable. Antenna: 70 feet. 
Cabinet size: Model 507, table, 30 x 131 x 14 inches. 
Model 508, console, 34 x 18 x 54 inches. Prices: Model 
507, $190 less accessories. Model 508, $320 with loud 
speaker. 

NO. 427. MURDOCK 7 

Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 trans- 
former and 2 resistance audio (two 01-A and 12 or 71). 
One control. Volume control: rheostat on r.f. Coils 
shielded. Neutralized. Battery cable. C-battery con- 
nections. Complete metal case. Antenna: 100 feet. 
Panel size: 9 x 23 inches. Price, not available. 

NO. 520. BOSCH 57 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71). One control calibrated in kc. Volume 
control: rheostat on r.f. Shielded. Battery cable. C- 
battery connections. Balanced. Output device. Built-in 
loud speaker. Antenna: built-in loop or outside antenna, 
100 feet. Cabinet size: 46 x 16 x 30 inches. Price: $340 
including enclosed loop and loud speaker. 

NO. 521. BOSCH "CRUISER," 66 AND 76 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71). One control. Volume control: rheostat 
on r.f. Shielded. C-battery connections. Balanced. 
Battery cable. Antenna: 20 to 100 feet. Prices: Model 
66, table, $99.50. Model 76, console, $175; with loud 
speaker $195. 

NO. 524. CASE, 61 A AND 61 C 

T.r.f. Semi-shielded. Battery cable. Drum control. 
Volume control: variable high resistance in audio sys- 
tem. Plate current: 35 mA. Antenna: 100 feet. Prices: 
Model 61 A, $85; Model 61 C, console, $135. 

NO. 525. CASE, 90 A AND 90 C 

Drum control. Inductive volume control. Technidyne 
circuit. C-battery connections. Battery cable. Loop 
operated. Model 90-C equipped with output device. 
Prices: Model 90 A, table, $225; Model 90 C, console, 
$350. 

NO. 526. ARBORPHONE 25 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 71). One control. Volume control: rheostat. 
Shielded. Battery cable. Output device. C-battery con- 
nections. Loftin-White circuit. Antenna: 75 feet. Panel: 
7} x 15 inches, metal. Prices: Model 25, table, $125; 
Model 252. $185; Model 253, $250; Model 255, combin- 
ation phonograph and radio, $600. 

NO. 527. ARBORPHONE 27 

Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A). Two controls. Volume control: rheostat. C- 
battery connections. Binding posts. Antenna: 75 feet. 
Prices: Model 27, $65; Model 271, $99.50; Model 272, 
$125. 

NO. 528. THE "CHIEF" 

Seven tubes; six 01-A tubes and one power tube. 
One control. Volume control: rheostat. C-battery con- 
nection. Partial shielding. Binding posts. Antenna: 
outside. Cabinet size: 40 x 22 x 16 inches. Prices: 
Complete with A power supply, $250; without acces- 
sories, $150. 

NO. 529. DIAMOND SPECIAL, SUPER SPECIAL, 
AND BABY GRAND CONSOLE 

Six tubes; all 01-A type. One control. Partial shield- 
ing. C-battery connections. Volume control: rheostat. 
Binding posts. Antenna: outdoor. Prices: Diamond 
Special, $75; Super Special, $65; Baby Grand Console, 
$110. 



RADIO BROADCAST ADVERTISER 



157 






ensations. 



STubelCont 



8 Tube 



RETAIL 



Big Discount to Agent* 
From this Price 



Has Complete A-B Power Unit 

A REAL ALL ELECTRIC Radio with one of 
the bet A-B power units on the market no 
batteries needed at, the world's lowest price. 
This Marwood can't be ex relied at ANY price. 
If you have electricity In your home, just plug 
into the light socket and forget batteries. >o 
more battery trouble and expense Costs less 
than c a day to operate. Always have lOO^ 
volume. ALL ELECTRIC Radios are high 
priced because they are new. We cut profit 
to the bone and offer a *250.0O outfit for 
$!>H.OO retail price. Big 1 discount to Agents. 
Don't buy any Radio 'til you get details of this 
sensational new ALL ELECTRIC Marwood. 



All Electric 

or Battery Operation 

AGAIN Marwood is a year ahead with the 
Radio sensation of 1928 at a low price that 
smashes Radio profiteering. Here's the sensa- 
tion they're all talking about the marvelous 8 
Tube Single Control Marwood for BATTERY or 
ALL ELECTRIC operation. Direct from the 
factory for only $69.00 retail price a price far 
below that of smaller, less powerful Radios. Big 
discount to Agents from this price. You can't 
beat this wonderful new Marwood and you can't 
touch this low price. Why pay more for less 
quality? To prove that Marwood can't be beat 
we let you use it on 30 Days* Free Trial in your 
own home. Test it in every way. Compare it 
with any Radio for tone, quality, volume, dis- 
tance, selectivity, beauty. If you don't say that 
it is a wonder, return it to us. We take the risk. 

New Exclusive Features 

Do you want coa.t to coast with volume enough 
to fill a theatre? Do you want amazing distance 
that only super-power Radios like the Marwood 
8 can gel? Do you want ultra-selectivity to cut 
out interference? Then you must test this Mar- 
wood on 30 Days' Free Trial. An amazing 
surprise awaits you. A flip of your finger 
makes it ultra-selective or broad just as 
you want it. Every Marw ood is perfectly 
BALANCED a real laboratory job. Its 
simple one dial control gets ALL the sta- 
tions on the wave band with ease. A beau- 
tiful, guaranteed, super-efficient Radio in 
handsome walnut cabinets and consoles. 
A radio really worth double our low price. 

Bay From Factory Save Half 

Why pay profits to several middlemen? A 
Marwood in any retail store would cost 
practically three times our low direct- 
from- the- factory price. Our policy is high- 
est quality plus small profit and enormous 
sales. You get the benefit. Marwood is a 
pioneer, responsible Radio, with a good 
reputation to guard. We insist on the best 
and we charge the least. If you want next 
year's improvements NOW you must get 
a Marwood the Radio that's a year ahead. 

AGENTS 

Make Big Spare Time Money 

Get your own Radio at wholesale price. It's 
euwy to get orders for the Marwood from 
your friends and neighbors. Folks buy 
Quick when they compare Marwood Quality 
and low prices. We want local agents and 
dealers In each territory to handle thf? enor- 
mous business created by our national 
advertising. Make #10O a week or more in 
spare time demonstrating: at home. No ex- 
perienre or capital needed. We show you 
how. Tills is the biggest season in Radio 
history. Kverybody wants a Kndlo. Get In 
now. Rush coupon for 3O days* Free Trial, 
beautiful catalog. Agents* Counde iitiul 
Prices and Agents' New Plan. 

MARWOOD RADIO CORP. 

5315 Ravenswood Avenue 
Department B- 1 7 Chicago, Illinois 



Get Our Discounts 

Before You Buy a Radio 

Don't buy any Radio "I ill you get our big discounts and 
catalog. Save half and get a Radio that IS a Radio. Try 
any Marwood on 30 Days' Free Trial at our risk. Tune 
in coast to coast on loud speaker with enormous vol- 
ume, clear as a bell. Let your wife and children oper- 
ate it. Compare it with any Radio regardless of price. 
If you don't get the surprise of your life, return it. We 
take the risk. Don't let Marwood low prices lead you 
to believe Marwood is not the highest quality. We 
have smashed Radio prices. You save half. 

6 Tube i Control 

This is the Marwood 6 Tube, 1 Control for BATTERY or 
ALL ELECTRIC operation. Gets coast to coast on loud 
speaker with great volume. Only $47.00 retail. Big dis- 
counts to Agents. Comes in handsome walnut cabinets 
and consoles. This low price cannot be equalled by 
any other high grade 6 tube Radio. Has the volume of 
any 7 lube set. If you want a 6 tube Radio you can't 
beat a Marwood and you can't touch our low price. 

$47 

RETAIL 
PRICE 
BigDiscount 
to Agents 
from This 
Price 



MARWOOD RADIO CORPORATION 

5315 Ravens wood Ave., Dcpt. IM7, Chicago, 111. 
Send Agents' Confidential Prices, 30 Days' Free 
Trial. New Catalog and Agents' New Money 
Making Plan. No obligation on my part. 




Name 



St. or R.F.D 

City State.. 



1.58 



RADIO BROADCAST ADVERTISER 



NO. 531. KOLSTER, 8A, 8B, AND 8C 

Eight tubes; 4 t.r.f. (01-A). detector (01-A), 3 audio 
(two 01-A and one 12). One control. Volume control: 
rheostat on r.f. Shielded. Battery cable. C-battery con- 
nections. Model 8A uses 50 to 75 foot antenna; model 
8B contains output device and uses antenna or detach- 
able loop; Model 8C contains output device and uses 
antenna or built-in loop. Prices: 8A, $185; 8B, $235; 
8C, 375. 

NO. 532. KOLSTER, 6D, 6G, AND 6H 

Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 12). One control. Volume control: rheostat 
on r.f. C-battery connections. Battery cable. Antenna: 
50 to 75 feet. Model 6G contains output device and 
built-in loud speaker; Model 6H contains built-in B 
power unit and loud speaker. Prices: Model 6D, $80; 
Model 6G, $165; Model 6H, $265. 

NO. 533. SIMPLEX, SR 9 AND SR 10 

Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 audio 
(01-A and 12). SR 9, three controls; SR 10, two con- 
trols. Volume control: rheostat. C-battery connections. 
Battery cable. Headphone connection. Prices: SR 9, 
table, $65; consolette, $95; console, $145. SR 10, table 
$70; consolette, $95; console, $145. 

NO. 534. SIMPLEX, SR 11 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 audio 
(01-A and 12). One control. Volume control: rheostat. 
C-battery connections. Battery cable. Antenna: 100 
feet. Prices: table, $70; consolette, $95; console, $145. 

NO. 53S. STANDARDYNE, MODEL S 27 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio 
(power tubes). One control. Volume control: rheostat 
on r.f. C-battery connections. Binding posts. Antenna: 
75 feet. Cabinet size: 9 x 9 x 19} inches. Prices: S 27, 
$49.50; S 950, console, with built-in loud speaker, 
$99.50; S 600, console with built-in loud speaker, 
$101.50. 

NO. 481. PFANSTIEHL 32 AND 322 

Seven tubes: 3 t.r.f. (01-A), detector (01-A), 3 audio 
(01-A and 71). One dial. Plate current: 23 to 32 mA 
Volume control: resistance in r. f. plate. Shielded 
Battery cable. C-battery connections. Output device. 
Antenna: outside. Panel: 17} x 8} inches. Prices: No. 
32 cabinet, $145; No. 322 console, $245 including 
loud speaker. 

NO 433. ARBORPHONE 

Five tubes; 2 t.r.f., detector, 2 transformer audio. 
All 01-A tubes. Two dials. Plate current: 16 mA. Vol- 
ume control : rheostat in r.f . and resistance in r.f. plate. 
C-battery connections. Binding posts. Antenna: taps 
for various lengths Cabinet size: 24 x 9 x 10 j inches. 
Price: $65. 



NO. 431. AUDIOLA 6 

Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). Drum control Plate cur- 
rent: 20 mA. Volume control: resistance in r.f. plate. 
Stage shielding. Battery cable. C-battery connection. 
Antenna: 50 to 100 feet. Cabinet size: 28J x H x 14i 
inches. Price not established. 

NO. 432. AUDIOLA 8 

Eight tubes; 4 t.r.f. (01-A), detector (00-A), 1 trans- 
former audio (01-A), push-pull audio (12 or 71). Bridge 
balanced t.r.f. Drum control. Volume control: resistance 
in r.f. plate. Stage shielding. Battery cable. C-battery 
connections. Antenna: 10 to 100 feet. Cabinet size: 
28J x 11 x 14j inches. Price not established. 

NO. 542 RADIOLA 16 

Six tubes; 3 t. r. f. (Ol-A), detector (Ol A), 2 trans- 
former audio (01-A and 112). One control. C-battery 
connections. Battery cable. Antenna: outside. Cabinet 
size: 16>/4 x 8'/ 4 x 7'A inches. Price: $69.50 without ac- 
cessories. 

NO. 456. RADIOLA 20 

Five tubes: 2 t.r.f. (99), detector (99), 2 transformer 
audio (99 and 20). Balanced t.r.f. and regenerative de- 
tector. Two dials. Volume control: regenerative. 
Shielded. C-battery connections. Headphone connec- 
tions. Antenna: 75 to 150 feet. Cabinet bize: 19 j x 
11 J x 16 inches. Price $115 including all tubes. 

NO. 457 RADIOLA 25 

Six tubes; five type 99 and one type 20. Drum con- 
trol. Super-heterodyne circuit. C-battery connections. 
Battery cable. Headphone connections. Antenna: loop. 
Set may be operated from batteries or from power mains 
when used with model 101 loud speaker. Price; $165 
with tubes, for battery operation. Apparatus for opera- 
tion of set from the power mains can be purchased 
separately. 

NO. 493. SONORA F 

Seven tube*; 4 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). Special balanced t.r.f. 
Two dials. Plate current: 45 mA. Volume control: 
rheostat in r.f. Shielded. Battery cable. C-battery 
connections. Output device. Antenna: loop. Console 
si,;e: 32 x 45J x 17 inches. Prices range from $350 to 
$450 including loop and loud speaker. 

NO. 494. SONORA E 

Six tubes; 3 t.r.f. (01-A), detector COO-A), 2 trans- 
former audio (01-A and 71). Special balanced t.r.f. 
Two dials. Plate current: 35 to 40 mA. Volume control: 
rheostat on r.f. Shielded. Battery cable. C-battery 
connections. Antenna: outside. Cabinet size: varies. 
Prices: table. $110; semi-console, $140; console, $240 
including loud speaker. 



NO. 530. KOLSTER, 7A AND 7B 

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio 
(01-A and 12). One control. Volume control: rheostat 
on r.f. Shielded. Battery cable. C-battery connections. 
Antenna: 50 to 75 feet. Prices: Model -7A, $125; Model 
7B, with built-in loud speaker, $140. 

NO. 495. SONORA D 

Same as No. 494 except arrangement of tubes; 2 
t.r.f., detector. 3 audio. Prices: table, $125; standard 
console, $185; "DeLuxe" console, $225. 

NO. 482. STEWART-WARNER 705 AND 710 

Six tubes; 3 t.r.f., detector, 2 transformer audio. 
All 01-A tubes. Balanced t.r.f. Two dials. Plate cur- 
rent: 10 to 25 mA. Volume control: resistance in r.f. 
plate. Shielded. Battery cable. C-battery connections. 
Antenna: 80 feet. Cabinet sizes: No. 705 table, 26t 
x 11} x 13}| inches; No. 710 console, 29| x 42 x 17? 
inches. Tentative prices: No. 705, $115; No. 710, 
$265 including loud speaker. 

NO. 483. STEWART-WARNER 525 AND 520 

Same as No. 482 except no shielding. Cabinet sizes: 
No. 525 table, 19} x 10 x 11} inches; No. 520 console, 
225 x 40 x 14 U inches. Tentative prices: No. 525, $75; 
No. 520, $117.50 including loud speaker. 

NO. 459. STROMBERG-CARLSON 501 AND 502 

Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 trans- 
former audio (01-A and 71). Neutrodyne. Two dials. 
Plate current: 25 to 35 mA. Volume control: rheostat 
on 1st r.f. Shielded. Battery cable. C-battery connec- 
tions. Headphone connections. Output device. Panel 
voltmeter. Antenna: 60 to 100 feet. Cabinet sizes- 
No. 501, 255 x 13 x 14 inches; No. 502, 28 !J x 50 
, 7 , x 16J inches. Prices: No. 501, $180; No. 502, $290. 

NO. 460. STROMBERG-CARLSON 601 AND 602 

Six tubes. Same as No. 549 except for extra t.r.f. 
stage. Cabinet sizes: No. 601, 27^ x 16J x 14A inches; 
No. 602, 28? x 51} x 19| inches. Prices: No. 601, $225; 
No. 602, $330. 

NO. 472. VOLOTONE VIII 

Six tubes. Same as No. 471 with following excep- 
tions; 2 t.r.f. stages. Three dials. Plate current: 2- 
mA. Cabinet size: 26i x 8 x 12 inches. Price $140. 

NO. 546. PARAGON "CONGRESS" 

Six tubes; 2 t.r.f. (01-A), detector (01-A), 3 impedance- 
coupled audio (two 01-A and 12 or 71). One main con- 
trol and three auxiliary adjustments. Volume control: 
resistance in r. f. plate circuit. Plate current: 40 mA. C 
battery connections. Tuned double-impedance audio am- 
plifier. Output device. R. F. coils are shielded. Cable or 
binding posts. Cabinet size: 7x18x9 inches. Price $90.00; 
without cabinet. $80.00. 




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llook'itp Book D- 2 



RADIO 

BROADCAST 








How to Use the Screen- Grid Tube 

A Directory of Manufactured Receivers 

Hints onOperatincftour CooleyRayfoto Receive 

The Phonograph Joins tKe Radio Receiver 

A Push-Pull Amplifier and B Supply 

Inside the Complete Receiver 



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STANDARD f OR ALL SETS 



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Radio sets and radio equipment make 
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owner of a radio will be delighted to re- 
ceive a set of new tubes. 

Buy them in combination of five or more. 
Your dealer will tell you the correct types 
of Cunningham Radio Tubes for which 
any radio set is designed. 

Don't use old tubes with new ones. 
Use new tubes throughout. 

E. T. CUNNINGHAM, Inc. 

New York Chicago San Francisco 



I 



RADIO BROADCAST ADVERTISER 



191 




Improve 
Reception! 



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\ PUSH-PULL amplifier in that last stage provides the speaker with ample 
** power to sustain a high volume level without tube overloading, transmit- 
ting the full effects of large swings in intensity common in orchestra music. 

This balanced type of amplifier draws no alternating current from the plate 
supply, a fact of great importance if socket power is used, as the impedance 
of the power unit does not affect the amplifier. This results in improved re- 
production of sustained notes, particularly of low frequency. 

Other advantages of the push-pull system are, a reduction in hum when al- 
ternating current is used for filament supply and for equal power outputs, a 
reduction in the plate voltage required. 

The amplifier is supplied completely wired. 

Type 441 amplifier 

For use with UX 226, CX 326, UX 171, CX 371, UX 210, or CX 

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Input inductance 30 henries. 

Input turns ratio i :2.25. 

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Price completely wired $20.00. 

Licensed by the Radio Corporation of America for radio amateur, experi- 
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license the unit may be sold only with tubes. 

GENERAL RADIO 

LABORATORY EQUIPMENT 
PARTS and ACCESSORIES 

If we can be of help to you in supplying technical 
information, we welcome your correspondence. Write 
for our Series A of amplification booklets describing 
various amplifiers, circuits and units. 



GENERAL RADIO CO. 



Cambridge, Mass. 



RADIO BROADCAST 



JANUARY, 1928 



WILLIS KINGSLEY WING, Editor 

KEITH HENNEV EDGAR H. FELIX 

Director of the Laboratory Contributing Editor 



Vol. XII, No. 3 



Cover Design *. From a. Design by Harvey Hopkins Dunn 
Frontispiece - ' - In the Laboratory of a Tube Manufacturer 194 
Radio Enlists the Helium Atom - Volney G. Mathison 195 



The March of Radio 



An Editorial Interpretation 198 



Can the Serious Problem of Radio Patents Be What Readers Say About Broadcasting 



Settled? 

The Prospects of a Patent Pool 
The Commission Announces a New Policy 



Conditions 
Broadcasting Bands Changed 
Broadcasting Notes 



The Commission Suggests Synchronization News of the Patent Field 



Schemes 



Among the Manufacturers 



Push-Pull Amplification Why? - Howard E. Rhodes 202 

The Phonograph Joins the Radio Set 206 

The Screened Grid Tube Keith Henney 208 

What Set Shall I Buy? - Edgar H. Felix 211 

"Our Readers Suggest 213 

Why I Installed a Cooley Picture Receiver - Edgar H. Felix 215 

Suppressing Radio Interference - - - A. T. Lawton 217 

Are Programs Going in the Wrong Direction? - John Wallace 219 

The Listeners' Point of View 

A Vacuum'Tube Voltmeter - The Laboratory Staff 221 

Radio Folk You Should Know 225 

(i.) Ralph H. Langley Drawing by Franklyn F. Stratford 

Some Fine Receivers and Their Chassis - 226 

"Strays" from the Laboratory - 228 

How Reliable are Short Waves? High-Powered Bunk 

Mathematics of the Audio Transformer New Apparatus 

Concomitants of Good Quality - .- 230 

How the "Synchrophase" Seven Was Developed John F. Rider 232 

As the Broadcaster Sees It Carl Dreher 235 

"Radio Broadcast's" Laboratory Information Sheets 238 

No. 153. Standard' and Constant-Frequency No. 157. Table for Wavelength-Freauency 

Stations Conversion 

No. 154. The na-A and 171-* Type Tubes No. 158. The Three-Tube Roberts Reflex 

No. 155. Wave Traps No. 159. Diagram of Three-tube Roberts 

No. 156. Wavelength-Frequency Conversion Reflex 

No, 160. Fading 

Manufacturers Booklets Available - - 244 

"Radio Broadcast's" Directory of Manufactured Receivers 246 

A Key to Recent Radio Articles E. G. Shall<hauser 255 

What Kit Shall I Buy? ..>'*, 257 



AMO^G OTHER THINGS. . . 

IT IS a sad duty to record the death of the Chairman of the 
Federal Radio Commission, Admiral W. H. G. Bullard, 
which occurred in Washington on Thanksgiving Day. Admiral 
Bullard, who served in the United States Navy for thirty-six 
years, for a very long time was close to the center of radio in 
almost all of its branches. His loss will be keenly felt, not only 
by those who knew him as a likable and able individual but 
especially by the Radio Commission itself. When the Radio 
Commission went to work on March 15, two of its members 
had a background of technical radio experience. These two men 
were Admiral Bullard and Colonel Dillon. Death has removed 
both. The Commission at this writing now consists of Acting- 
Chairman E. O. Sykes, O. H. Caldwell, Sam Pickard, and 
H. A. Lafount. Not one of these members has a technical radio 
background which would enable them to better struggle with 
the complicated problems which confront them. 

THE reports of international conferences, on whatever 
subject, usually make rather dull reading for the general 
public and the Washington Radio Conference has beer. 11O 
exception to this rule. The proceedings may not be exciting, but 
the results are certainly important. There has been no revision 
of international agreement since the London conference of 1912, 
and radio progress has been so rapid since then that the articles 
of that Convention were hopelessly inadequate to meet present 
needs. There have been many rocks and shoals in the way of 
the present conference, which, at this writing, has just wound 
up its work, but through good management and a praiseworthy 
desire for general accord, the delegates have succeeded in 
drawing up a Convention which well meets the needs of radio 
today. Not the least important decision reached at Washington 
was that dealing with the international assignment of channels 
in the frequency spectrum. In that respect, we are glad to note, 
the future needs of short-wave communication, broadcasting, 
commercial, and amateur work were provided for. The ama- 
teurs had a hard fight, but room has been saved for them a 
result of which the broad-minded directors of the American 
Radio Relay League may well be proud. 

THE issue of RADIO BROADCAST before you contains some 
extremely interesting articles. The story by Howard 
Rhodes on the problems of push-pull amplification is distinctly 
helpful and should cast much light on a form of amplification 
which is again being revived after several years of comparative 
disuse. . . . Those who are anxious to know what the new 
screened-grid tube will do will find Keith Henney 's article very 
valuable indeed. As soon as possible, RADIO BROADCAST will 
give its readers data on receiving circuits which can be used 
with the tube; the latter has just been released for general sale. 

THOSE of our readers who would like to have their names 
forwarded to the manufacturers of the special apparatus 
necessary to construct a Rayfoto receiver may send letters to 
the undersigned, and printed matter containing detailed in- 
formation will be sent them. . . . The next RADIO BROADCAST 
will contain an article describing a new super-heterodyne, 
entirely operated from a. c., which has much to recommend it, 
both from the design and appearance point of view. There 
will also be many other articles of interest. 

WILLIS KINGSLEY WING. 



Doubleday, Page & Co. 

MAGAZINES 
COUNTRY LIFE 
WORLD'S WORK 
GARDEN & HOME BUILDER 
RADIO BROADCAST 
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EDUCATIONAL REVIEW 
LE PETIT JOURNAL 
EL Eco ' 
FRONTIER STORIES 
WEST WEEKLY 
THE AMERICAN SKETCH 



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OOUBLEDAT, PAGE & COMPANY, Garden &ty, 

Copyright, 1927, in the United States, Newfoundland, Great Britain, Canada, and other countries by Doubleday, Page 

TERMS: $4.00 a year; single copies 3? cents. 

192 



Doublfday, Page & Co. 
OFFICERS 

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Company. All rights reserved. 



RADIO BROADCAST ADVERTISER 



193 



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THORDARSON 210 TYPE 
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This amplifier, mounted on a special metal chassis, uses the 
Thordarson Power Compact R-21Q. Provides "A," "B," and 
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In the Laboratory of a Tube Manufacturer 



Where diligent investigation precedes production of any new kind of tnhe 



likely as not, discarded. It is said that about 99 per cent of these hand-mud., 
expcnmental tubes are discarded without even bei , K put into prudSot ton Whin 
we cons,der the expense of such tireless research, more and ,,,"",!, we' recog 
m*. the og,c ,,f ,he statement that it is only ,he larger and more "moneyed*' 
manufacturers who are capable of producing dependable radio equipment 



194 







STUDYING GASES IN THE LABORATORY 

Looking into the depths of ionized helium atoms with a spectroscope. Charles Grover Smith, 
who is shown in this picture, spends considerable of his time studying gases, especially helium 

RADIO ENLISTS THE HELIUM ATOM 

By VOLNEY G. MATHISON 



IT'S all so useless, that's why I'm quitting," 
complained the young college graduate to 
the chief of the laboratory in which he had 
lately gotten a job. "What can ever come out of 
measuring the ohmic resistances of a cubic mil- 
limeter of about a million different substances 
under a couple of hundred different tempera- 
tures? That's the job you've given me nothing 
but an endless measuring of ohms. -If this is 
what you call scientific research 

"It is," interrupted the electro-chemist. 
" It's the backbone of it prolonged patience at 
tedious work." 

"Seefns tedious enough. But I could stand that 
if I could see some results ahead. I can't see 
any." 

"Well, there may be no directly important 
outcome of what you're doing. You are simply 
adding to the stock of scientific knowledge in a 
prosy way, working on a huge book of tempera- 
ture-resistance tables. You can't tell in advance 
what it may lead to. Take, for example, the 
helium-gas rectifier tube used in radio B-supply 
devices. It was never invented, it just grew out 
of a lot of laborious work like this. American 
factories are turning out about 20,000 of these 
tubes a day at present and the patent profit is 
close to a dollar and a half apiece. There's a 
return to pure research at the rate of something 
like $30,000 a day. That soon pays for a lot of 
slow laboratory grinding, doesn't it?" 



"Yes," reiterated the young graduate, "but 
that tube wasn't developed by any such work as 
I'm doing here measuring the resistances of 
rust, rocks, roots, cocoanut shell, and the end 
years away. It's all so discouraging!" 

As a matter of fact, the helium-gas tube for 
B-devices was the result of a great amount of 
purely scientific work of the tedious and rather 
unfocussed sort that this discouraged young 
chemist was assigned to, though, perhaps, the 
experiments involved were a good deal more 
technical. A few years ago we began studying 
the actions of electrons in gases. At that time 
nobody knew much about electrons maybe we 
don't yet and the experiments were entirely 
general in kind. The aim was to find out some- 
thing, not to invent something. One young fellow 
had the job of finding out definitely whether or 
not electrons emitted from a cathode into a tube 
of gas passed through the gas without colliding 
with its atom centers. 

An atom of any kind of substance, as nearly 
every one now is aware, consists of a group of 
protons and electrons surrounded by planetary 
electrons. The space in between seems to contain 
nothing but electric tension, though now late in 
1927 we are about to believe that this tension 
consists of a flurry of particles called etherons 
that are so small they make an electron look 
like a balloon in comparison with an apple, and 
move almost twice as fast as light. Matter.even 

"95 



solid steel, is nearly all emptiness, and it is the 
crudeness of our undeveloped physical senses 
that makes us think otherwise. 

So this young man set about trailing a lot of 
wandering electrons through a wilderness of gases 
to find out what they did in there. He had a 
photographing outfit that would show the paths 
of the electrons. Many gases and pressures had 
to be tried. In one series of experiments each 
photograph showed the flight of 200,000 elec- 
trons, and that young man took 100,000 photo- 
graphs separately, one after the other, before he 
got one collision of an electron with the middle 
of an atom of the gas under test. He kept on, and 
got a total of eight collisions in 400,000 photo- 
graphs. Even when it is possible to use a fast 
automatic machine to take such photographs, 
they all have to be individually and laboriously 
examined. 

The photographer found out something else. 
He found out that when an electron hit an atom 
of gas square in the middle, it blew the atom to 
pieces, producing a shower of unattached elec- 
trons, and unsmashable groups of electrons and 
protons that were named alpha particles. Alpha 
particles were identified with a spectroscope as 
being the same as a mysterious gas which had 
been seen by astronomers pouring over the sun, 
and which they had named helium a "sun" 
word. 

The alpha particles or helium atoms can be 



196 



RADIO BROADCAST 



JANUARY, 1928 



quite easily robbed temporarily of one planetary 
electron, but they cannot be further broken up 
except with the most extreme difficulty. Helium 
gas was therefore recognized as a valuable elec- 
trical conducting medium that would tend to 
act at all times with unchanging properties and 
that would refuse to eat, corrode, or combine in 
any way with the metal tips of the electrodes by 
which electricity would be fed into the gas. No 
particular electrical use for this gas had yet 
been thought of, though it was proposed that 
metal-ended glass cartridges of helium might be 
valuable as ultra-stable resistors capable of 
withstanding enormous currents and pressures. 

In photographing the flights of electrons 
through helium gas, it was observed that, when 
an electron struck an atom of helium, the elec- 
tron ran off with one of the planetary electrons 
of the helium atom, carrying it to the anode. 

A sketch of this performance would be almost 
inconceivably out of proportion 
since there would have to be rep- 
resented the trillions times trillions 
of atoms in the tube, while elec- 
trodes about the size of the state 
of Georgia would be necessary to 
preserve the proper scale if the 
atoms were one half inch across. 
If the helium nucleus were drawn 
the size of a pea, the planetary 
electrons would properly be placed 
a quarter of a mile away. Such is 
the ghastly emptiness of matter 
of even the "solid" walls of a 
glass tumbler from which we drink 
billions of electrons and protons in 
the peculiarly ordered state we call 
water; and of the stout iron bars 
upon which the jail-bird leans his 
head. But solidity, although physi- 
cally an illusion, is nevertheless real 
because it is a manifestation of 
a powerful electrical condition. 

To return now to the story of 
the doings in the helium tube un- 
der electrical pressure, we learn 
that the unfortunate gas atom that 
has lost an electron is said to be 
"ionized." This is all that ioniza- 
tion means, i. e., a breaking away 
of electrons from gas atoms. It, 
the ionized atom, is over-positively 
charged and flies with terrific force 
toward the negative or cathode 
element, which it strikes violently 
and from which it extracts an 
electron from the inflowing stream 
in the wire leading to the cathode 
the entrance element from the outside supply. 
The gas atom, now once more in a normal state, 
rebounds from the cathode and flies about 
jubilantly until it is again robbed of an electron, 
when it instantly goes through the perform- 
ance just described all over again. 

One remarkable thing about this action which 
is not yet understood is the fact that the bom- 
bardment of the cathode by ionized gas particles 
causes a liberal release of free electrons of extra 
electrons beside those taken to balance the 
ionized atoms. In other words, by hammering a 
negative electrode with positively charged gas 
particles, we get a discharge of electrons. Per- 
haps the "yanking" out of the electron needed 
by the atom for itself is so violent that several 
extra electrons are hustled out along with it. 

Some of these extra electrons in their flight to 
the positive or exit element collide with other gas 
molecules, and the action, the pounding of gas 
particles on the cathode and the emission of elec- 
trons, is continuous as long as electrical pressure 
is applied to the device. A current consequently 



flows through the tube. In this manner elec- 
tricity gets through a cold-electrode rectifier 
tube. 

HOW A TUBE RECTIFIES 

HpHE foregoing does not explain how current 
* gets through the tube in only one direction. 
It would seem that, when the tube is put in an 
a. c. circuit, each element would become alter- 
nately an anode and a cathode, an exit and 
an entrance, and that the flow would be equally 
back and forth through the gas in the tube. 
But since the current flow depends upon hitting 
an electrode with gas particles, it becomes ap- 
parent that, by making one electrode big and the 
other one little, you can facilitate the hitting in 
one direction and minimize it in the other. When 
the larger electrode is negative, it will get thor- 
oughly hammered with gas particles and will 
release many electrons; consequently, a large 




BEHIND THE SCENES IN THE LABORATORY 

Preparing a globe of pure helium for research experiments. This kind of 
work never stops, and in every progressive tnbe concern, the laboratory 
is always ahead of the factory is always working on " something better." 



current will flow through the device. On the other 
hand, when the smaller electrode goes negative 
under the reversing a. c. current, it will not be 
battered so much by the flying gas particles as 
the other electrode was and therefore will not 
emit many electrons. A small current will, how- 
ever, flow. The big electrode is a better emitter 
because it has more surface for the gas particles 
to "rip" electrons out of. When the big electrode 
is positive and the small electrode is negative, 
the ionized gas atoms do fly toward the small 
electrode but most of them miss it because it 
is comparatively hard to hit. Some particles 
strike the small element while it is negative and 
release electrons which fly across to the large 
electrode. This produces a "back-current" 
through the tube. All helium-gas rectifier tubes 
have this "back-current." The amount of it 
determines the efficiency of the rectifier and it 
usually is but a small percentage of the current 
in the other direction. 

The "back-current" is reduced by making 
the anode small and hard, while the other large 



electrode is treated with radioactive earths to 
encourage it to release electrons. Besides the 
difference in size of the bombarding areas of the 
two elements, the electric field produced by the 
smaller electrode is less attractive to the ionized 
gas particles than that of the larger one, with the 
result that it is hit less violently. 

Both of the elements are made principally of 
nickel, which has been purified in a hydrogen 
furnace to remove all impurities. 

The description so far has dealt with a tube in 
which there are only two elements. The usual 
helium-gas rectifier tube has three elements 
a hat-shaped or tubular cathode and two anodes. 
This is simply two rectifier tubes in one, using a 
common cathode, and enables both halves of the 
a. c. wave to be used. The action here is exactly 
the same as that already described, except that 
the emission of electrons is alternately from the 
cathode to first one anode and then to the other 
to each one as it becomes positive 
in turn. And the cathode is almost 
continuously under bombardment, 
because it is always negative with 
respect to one anode or the other. 
At the same time that the flight of 
electrons takes place from the 
cathode to the positive anode, a 
"back-current" emission travels 
from the temporarily negative 
anode toward the cathode. Some 
electrons also fly between the two 
anodes, causing "leak" current. 
These "leak" and "back-cur- 
rents," while not wanted, cannot 
be entirely eliminated, and as long 
as they are small, cause no serious 
trouble. In the factories, each tube 
is tested on a machine that meas- 
ures the "back-current," and if 
excessive, the tube is discarded. 
Too much "back-current" through 
a tube will cause a B-device to 
hum. 

It is worth pointing out that the 
popular 'conception of the move- 
ment of electricity through a B- 
device rectifier and filter system 
is erroneous. The general idea is 
that a "positive current" gets 
across the rectifier tube into the 
filter where it is tanked arid choked 
into smoothness. But it should be 
remembered that current is purely 
electronic flow it consists only of 
moving electrons in a conductor 
and these electrons flow only from 
negative to positive. It is very con- 
fusing to the novice and entirely unnecessary to 
say that the current flows one way and the elec- 
trons the other. There is no such current flowing 
against the movement of the electrons. It simply 
doesn't exist. In the early days of electrical 
science, long before any kind of a radio vacuum- 
tube had even been thought of, experimenters 
misunderstood some of the actions of electricity, 
and the positive-to-negative idea of current flow 
was one of the consequences of their lack of 
knowledge. In the business of science, there is 
no sensible reason for compromising with mis- 
takes or twisting them around to meet new facts, 
as is being attempted all the time in religion; 
they should be simply left out of the story. 

The electrons flowing in a B-device circuit 
enter the negative wires, pass direct to the fila- 
ments of the vacuum-tubes in the radio receiver, 
are emitted from the hot filaments to the plates, 
pass from the plates through the various circuits 
to the positive lead of the B device, thence 
through the chokes to the cathode element of the 
rectifier tube, and from this point they are 



JANUARY, 1928 



RADIO ENLISTS THE HELIUM ATOM 



197 



sprayed alternately to the anode elements as 
these become positive in turn under the inductive 
action of the a. c. current in the primary power- 
supply windings. The filter chokes and tanks pre- 
vent a voltage and current fluctuation in the 
line during the intervals between the spraying 
or emission surges through the rectifier tube. 

So deeply ingrown is the current-flow con- 
ception that in a recent issue of a well-known 
radio magazine there was a cut of a helium-gas 
tube with the hat-shaped cathode marked 
"anode" and the two anodes marked "cath- 
odes." The accompanying text used the same 
terminology, which was wrong even in the light of 
the old theory. It should be clear that the posi- 
tive side of a B-device filter is of negative 
potential compared to the ends of the secondary 
winding of the power transformer to which the 
rectifier-tube anodes are connected. The large 
cathode of a helium rectifier is equivalent to the 
incandescent filament of the filament type tube. 

WHY A TUBE DETERIORATES 

CINCE the helium-gas rectifier tube contains 
^ no heated filament emitter to burn out or 
become lifeless through deterioration, many 
usersof thedevice feel that it ought to last almost 
forever for years and years at any rate, and 
wonder why it sometimes has a short life. 

As a matter of fact, the developers of the tube 
themselves thought at first that it would have a 
life of 10,000 hours or more of continuous use, 
but soon found that such was not the case. The 
principal thing that brings the life of a helium- 
gas rectifier tube to an end is the fact that the 
helium gas in the bulb disappears. Helium gas is 
inert, it will not combine with anything, so far 
as we know at present; it is genuinely strange, 
therefore, that it should disappear from a her- 
metically-sealed bulb. It seems that the ionized 
gas particles pound the cathode with such force 
that some of them are driven deep into the metal 
and stay there become occluded or imprisoned. 

After a certain length of time so many gas 
atoms are bound in the metal that the tube be- 
comes very hard, the vacuum rises, and the 
bombardment of the cathode becomes meager, 
owing to the reduced number of molecules of 
gas to do the battering. The current output of 
the tube then falls off to such a point that it 
must be discarded. 



The life of many a good helium-gas tube has 
been quickly brought to an end through the 
breaking down of condensers in filter circuits. 
Cheap inferior condensers in both home-made 
and factory-built power devices usually go to 
pieces after a few weeks or months of use, with 
the result that the rectifier tube is placed in a 
dead short-circuit. The heavy current flow 
quickly burns off the tips of the anodes in the 
tube. The helium gas itself cannot be injured by 
any current. Helium gas will carry currents so 
great that they will instantly explode copper 
conductors of the same cross-sectional area; 
but under such currents the gas particles quickly 
drive themselves deep into the negative elec- 
trodes and are as good as lost. 

Some of the cheaper helium-gas tubes now on 
the market may be short-lived through the 
presence of impurities in the helium, which would 
destroy the electrodes. Extremely pure helium 
must be used. This gas is purified by passing it 
through copper tubes filled with cocoanut char- 
coal and maintained at the temperature of liquid 
air more than 250 below zero, Fahrenheit; then 
to a steel reservoir; then to a second battery of 
tubes of charcoal surrounded with liquid air 
to remove oxygen or nitrogen which might come 
away from the walls of the reservoir. The helium 
is admitted until the charcoal is partly loaded 
with it; next it is pumped off with vacuum 
pumps and the impurities remain in the char- 
coal, which is itself purified and used over again. 

It is interesting to consider that absolute 
purification of anything, liquid, gaseous, or solid, 
is almost impossible. Imagine for a moment that 
you could mark molecules in some such way 
that you could identify them when you saw them 
again. Assume that you took a glass of water 
with the molecules of water all thus marked and 
stirred it into the waters of the oceans of this 
earth, that you waited a couple of million years 
for thorough mixture, and that you then walked 
up to the nearest hydrant in your vicinity and 
casually drew a glass of water, you would find 
about 2000 of your marked molecules in it! Of 
course, we may be a few molecules out on this 
estimate, but that is roughly the correct mathe- 
matical number, because there are 2000 times 
as many molecules in a glass of water than there 
are glasses of water on the earth. 

Again, molecules of air, if admitted into a 



highly-evacuated 25-watt electric light bulb 
through a hole so small that they had to flow in 
single file, would take about 100,000,000 years 
to fill it to atmospheric pressure. A little re- 
flection will show that "purity," like everything 
else, is probably only a relative condition. 
"Some of 'em is more pure, and some of 'em is 
less pure, but none of 'em is all pure," said the 
sour cynic, and while he wasn't speaking of gases, 
and was not a scientist for that matter, he was 
uttering profound truth. 

THE TIN "HAT" 

VA/HAT is the queer tin "hat" for in the 
* " modern gaseous rectifier tube? Nobody 
outside of the research laboratories 'seems to 
know. Even some of the "bootleggers" making 
these tubes don't know. 

In the early experimental forms of the helium- 
gas tube, great trouble was met with owing to 
the disruption of the cathode element under the 
hammering of the ionized gas atoms. The earlier 
tubes had disk shaped cathodes, and the gas 
atoms pulled out electrons with such violence 
that tiny pieces of solid metal were often ripped 
loose from the electrode. These metal bits were 
thrown against the glass walls of the tube, 
blackening it, and resulting in the speedy 
destruction of the cathode. 

For this reason the peculiar tin-hat form of 
cathode was evolved because, with this arrange- 
ment, the bombardment of the cathode and emis- 
sion of electrons is entirely internal. The action 
all takes place inside of the electrode. If a bit of 
metal is torn from the cathode at any point, it is 
hurled across the inner chamber and thrown 
back onto the element somewhere else. There is 
no loss of metal because the cathode is continu- 
ally built up as fast as it is torn down. 

It seems that, if we, as human beings, could be 
temporarily reduced to the size of, say, an atom, 
together with a corresponding ability to see 
small objects, and were then placed upon the 
cathode of an operating helium-gas rectifier tube, 
we would have an impression of standing among 
ranges of heaving mountains of metal in a state 
of furious convulsion and uproar, bombarded 
with enormous meteors of helium and full of 
volcanic upheavals and earthquake-like shocks, 
while electrons would arise like clouds of steam 
on all sides, or spurt out like fiery sparks. 



. 




A VIEW OF THE LABORATORY IN WHICH THE HELIUM-GAS RECTIFIER TUBE WAS PERFECTED 



I HI- MA 






NFWS AND INimPKHATIQN OF r.UUUI-'NT UAmQ KVHNI I V~ 

Can The Serious Problem of Radio Patents Be Settled? 



THE recent adjudication of several 
important patents, such as those of 
Hazeltine and Alexanderson, has 
forced upon the radio industry the long 
deferred day of reckoning with inventive 
genius. Conscientious and established man- 
ufacturers have proceeded promptly to ob- 
tain licenses under Radio Corporation 
patents which make available to them the 
work of some of the world's greatest labora- 
tories. By assuming an annual royalty 
guarantee of one hundred thousand dollars 
a year, charged at the rate of 75 per cent, 
of the cost of radio receivers, they become 
licensed under R. C. A., A. T. & T., West- 
ern Electric, General Electric, Westing- 
house and Wireless Specialty patents. 

Having assumed this substantial burden, 
the licensees considered their patent diffi- 
culties disposed of. But some quickly found 
that licenses under Hazeltine and Latour 
patents are also necessary to freedom from 
patent difficulty and, probably quite re- 
luctantly, signed the Hazeltine licenses with 
the additional burden of a 25 per cent, 
royalty and an annual guarantee of thirty 
thousand dollars a year. This duty per- 
formed, the manufacturer dismissed patent 
trouble and consecrated himself to the 
problem of selling newer and better radios. 
And then came the independent inventor 
to disturb his peace of mind. Old patents 
were dug up, demanding recognition. New 
patents, just issued, added to the swarm. 
Some of these inventions are as worthy of 
recognition as those covered by the Radio 
Corporation license. Others may be worth- 



less and which will not withstand the test 
of adjudication. 

The weary manufacturer's answer to 
those demanding additional royalties is be- 
coming less and less courteous. He is now 
paying all that the traffic will bear. Unless 
some remedy is offered, his answer to patent 
holders soon will be: "A plague upon your 
patents!" 

The Prospects of a Patent Pool 

SOME manufacturers have united in de- 
fensive groups to protect themselves 
against the swarm of inventions which 
now confronts them. They foresee the neces- 
sity for so great an increase in the price of 
radio receivers by reason of patent royalties 
that the public will no longer be able to 
afford them. Faced with the alternatives of 
excessive royalties or occasional injustice 
to the legitimate inventor, the manufac- 
turers have, quite naturally, tended to the 
latter course. 

No doubt, some of the inventors, whose 
claims for royalties are being disregarded 
or opposed, will eventually win adjudica- 
tions, and triple damages, if they are suf- 
ficiently patient and prosperous to afford 
the protracted legal battle which must pre- 
cede such a result. It is quite possible that 
combined resistance to the inventor may, 
in some cases, prove costly, because it is 
not reasonable to assume that Radio Cor- 
poration, Latour and Hazeltine patents 
are the only ones which will be favorably 
adjudicated. 

Combined resistance, however, is the only 



course open to the manufacturer because 
there are too many unadjudicated patents 
demanding attention. It would be suicidal 
to agree to a license under all of them; the 
cost of radio sets to the consumer would 
double and sales resistance would fourfold. 

Most of the executives in the radio field 
wish to concentrate their attention on the 
design, manufacture and merchandising of 
radio equipment, but patent problems now 
require an alarming proportion of their 
time. Naturally, the leaders of the radio 
industry are nervous. At every trade con- 
vention and meeting, we hear talk of an 
all-inclusive patent pool. 

Unfortunately, no patent pool can be 
successfully organized unless it has the 
unanimous support of all radio manufac- 
turers and patent holders. To relieve the 
patent situation economically and pain- 
lessly, there must be a single, powerful, 
radio trade organization. Nevertheless, the 
N. E. M. A. and the R. M. A. still to 
all outward appearances indulge in short- 
sighted rivalry. An unofficial canvass of 
ninety per cent, of the membership of one 
of these organizations reveals that all but 
two were in favor of consolidation. To make 
a consolidation possible, one or two leaders 
in the R. M. A. must for a moment forget 
that their organization has the largest 
number of members and the youngest 
blood, and one or two members of the 
N. E. M. A. must forget some remarks 
made several years ago over matters long 
since settled. And both groups must cease 
suspecting each other. 




CHANGES IN THE FEDERAL RADIO COMMISSION 



Hcmy Miller 



Henry A. Bellows, Sam Pickard.and Carl H. But man. Commissioner Bellows was appointed from the Minneapolis district where he had long ably managed 
wcco. His resignation, effective November ist, left a vacancy which was filled by the President in appointing Sam Pickard who has been Secretary to 
the Commission since its appointment. Carl Butman is the new Secretary succeeding Mr. Pickard and has many years of experience in Washington as 
news correspondent, specializing in radio, to aid him in his new post. Mr. Butman has for some time been Washington correspondent for RADIO BROADCAST 

,98 



JANUARY, 1928 



ACTIVITIES OF THE RADIO COMMISSION 



199 



The industry is headed for one of the 
most dangerous shoals in its career. Doubt- 
less, it will weather it successfully. But 
how long the shoal will impede its progress 
depends upon how successful it is in placing 
the ship in the hands of one pilot, instead 
of two squabbling deck hands, to guide it 
past the patent whirlpool. It will require 
leadership of the highest order to establish 
a patent pool. 

In the future, there will be a new and 
greater industry, much greater than we 
imagine to-day. The radio receiver is but 
a nucleus of a home entertainment device 
which will rival the automobile in useful- 
ness and entertainment value and, in the 
end, its gross sales figures will be as large 
as those of the envied motor car industry. 
The radio receiver, the phonograph, the 
motion picture machine and the television 
receiver will, some day, be available in a 
single, compact, home-entertainment de- 
vice. The public will pay as much for a 
versatile means of home entertainment as 
for an automobile to take them away from 
home. The more the leaders of the radio 
industry concentrate upon the develop- 
ment of radio and the establishment of its 
true market, the sooner they will have a 
five-billion-dollar industry. At present, the 
most vital aid in that objective would be 
turning over radio's patent problems to a 
patent pool. The alternatives are continued 
squabbles, continued patent fights, and a 
radio market still limited to about ten per 
cent, of the American public. 

The Commission Announces a 
New Policy 

THE Federal Radio Commission re- 
cently announced a long list of al- 
location changes which have been 
made with the purpose of improving the 
channels of a few of the leading stations of 
the country. The Commission it is ru- 
mored, will hereafter work on the theory 
that there are a few leading, national sta- 
tions, which are the favorites of listeners 
all over the country and therefore deserve 
clear channels, entirely free of interference 
to the limit of their range. This is the basis 
upon which several years ago Secretary of 
Commerce Hoover worked out the plan of 
Class A and Class B broadcasting stations 
and urged on the commission in these 
columns for more than a year. 

Following this plan, WHAZ, which shared 
time with WGY, was shifted to share time 
with WMAK, giving powerful and popular 
WGY a full channel. WJAR, Providence, was 
shifted from 620 kc. to 800, eliminating 
widespread heterodyning with WEAF, ten kc. 
off, experienced throughout southern New 
England. WEEI, Boston, was shifted from 
670 to 650 kc., avoiding a heterodyne im- 
posed upon it by a Chicago station. WTRL, 
a little station in Tilton, New Hampshire, 
formerly occupying a channel adjacent to 
wjz, was shifted downward in order to 
eliminate a whistle which it thrust on wjz's 
carrier in large parts of New England. 
WDWM of Asbury Park, New Jersey, was 



shifted so as to eliminate conflict with 
WSAI'S carrier. WNAC of Boston and WEAN 
of Providence, Columbia chain members, 
were made channel-sharing stations, prob- 
ably in the interests of better management, 
and moved quite far into the unpopular 
higher frequency region. WCAU, a Philadel- 
phia advertising station and now a mem- 
ber of the Columbia network and WKRC of 
the same chain were demoted from the 
lower frequency region. WOR now has wos 
of Jefferson City, Missouri, as a channel 
neighbor instead of wsui, Iowa City. We 
believe the Missouri station is more power- 
fully received in Newark and will therefore 
accentuate slightly the whistle which 
already mars WOR'S programs. 

Another station to benefit by the Com- 
mission's reallocation is KSD, St. Louis, 
which is given full time. KSD is one of the 
pioneers of broadcasting and is deserving 
of the consideration which the Commission 
has shown. 

The conclusion that N. B. C. stations 
have fared better than Columbia chain 
stations is inescapable, but it must not be 
forgotten that the former do include most 
of the pioneer stations of the country which 
have served faithfully and well for years, 
while most of the latter have not yet won 
their spurs in public estimation. Clearing 
the channels of the N. B. C.'s leading sta- 
tions cannot be criticized, but it might have 
been better policy to have concentrated 
less on Columbia stations when the de- 
moting process was begun. 



The Commission Suggests 
Synchronization Schemes 

IN A speech before the American In- 
stitute of Electrical Engineers, Com- 
missioner O. H. Caldwell made some 
remarks about the problems of maintaining 
a broadcasting station on its assigned fre- 
quency. He mentioned three methods of 
accomplishing this purpose, one well known 
and widely used, one successfully used ex- 
perimentally but economically prohibitive, 
and a third which is a rather unfortunate 
suggestion. It is the Commissioner's idea 
that, if complete frequency stability could 
be secured and the heterodyne interference 
between stations now assigned to the same 
channels eliminated, more stations could 
safely occupy the same channel. While this 
is true, it must be realized that the audio- 
frequency components of two stations on 
the same channel also affect each other. 
When the distant station does not come in 
with sufficient volume to cause cross talk, 
it often causes irregular distortion. 

Cyrstal control, the first method sug- 
gested for synchronizing carriers, is not 
sufficiently stable to solve the problem. 
Temperature and humidity changes affect 
the frequency of the crystal and, conse- 
quently, it does not give the absolute regu- 
lation necessary for successful occupancy 
of the same channel by two broadcasting 
stations whose carrier ranges overlap. 

The second method suggested, the use of 
a wire circuit for the transmission of a con- 




A WIRELESS STATION IN 1904 

A 35-kw. spark transmitter was erected by the old De Forest Company for the Navy near San Juan, 
Porto Rico. The illustration shows the receiving installation with Mr. Irodell, operator for the De 
Forest Company using the receiving equipment which consisted of a "pancake" tuner and an electro- 
lytic detector. It was not until 1906 that a carborundum detector was substituted for the electro- 
lytic one. The call signal of this station, which may be recalled by old-timers, was SA. 



200 



RADIO BROADCAST 



JANUARY, 192! 



trolling frequency, which has been success- 
fully employed by WBZ and WBZA at 
Springfield and Boston, has the disadvan- 
tage of being prohibitively expensive. For 
example, if WOR attempted to eliminate the 
heterodyne whistle caused by wos at 
Jefferson City by this method, it would 
probably cost some fifty thousand dollars 
a year. To stabilize the whole broadcasting 
structure would require perhaps five years 
to erect sufficient telephone channels for 
the purpose and an expenditure of perhaps 
twenty million dollars a year in mainte- 
nance. 

The third suggestion made by the Com- 
missioner was prompted by a suggestion 
from WDRC of New Haven, Connecticut, 
a 5OO-watt station. A heterodyne whistle, 
originating from the carrier of WAIU, a 
jooowatt station in Columbus, Ohio, 
about 500 miles distant, had been suffi- 
ciently annoy ing to require drastic measures. 
To solve this problem, a receiving station 
was installed five miles from New Haven, 
connected by wire lines with WDRC'S trans- 
mitter. By tuning this receiving set care- 
fully so that the heterodyne whistle is 
eliminated, WDRC'S carrier is adjusted to 
coincide with that of WAIU. So long as the 
operator is vigilant and skillful, there is no 
heterodyne whistle. 

But, if the whole broadcasting structure 
depended for frequency stability upon 
manual control, it would become a sorry 
mess. One need but recall the days of the 
regenerative receiver, with its heterodyning 
carrier of but a tiny fraction of a watt. 
Then imagine manually controlled broad- 
cast transmitters with hundreds and thou- 
sands of watts power, trying to establish 
zero beat with each other. The incident 
again emphasizes the fact that the Com- 
mission is sadly in need of technical assist- 
ance which will help the members to grap- 
ple more wisely with their problems. Any 
competent engineer could have pointed out 
the dangers of this ingenuous panacea. 



What Readers Say About Broad- 
casting Conditions 

THE following are quotations from readers 
of these editorials. George Madtes, Radio 
Editor of the Youngstown Vindicator, 
writes: "1 have no doubt that the re-allocation 
of frequencies has materially helped stations in 
New York and Chicago, but it has not attained 
the Commission's apparent goal an arrange- 
ment which would permit listeners everywhere to 
enjoy the stations nearest them. We are within 
fifty miles of stations in Cleveland, Pittsburgh 
and Akron and depend upon them for local 
service. Our four main stations in these cities, 
WTAM, KDKA, WCAE, and WADC are often hetero- 
dyned and WADC and WCAE are almost invariably 
useless at night." 

W. W. Muir of Lockport, New York writes: 
"One cannot help but notice the difference be- 
tween the stations which are operating in the 
few wave bands on which there is only one station 
and those operating on the frequencies on which 
there are more than one station. The stations 
which are operating on exclusive channels are 
usually free from distortion, the signal being 
strong and clear. The stations which are operat- 
ing on wavelengths on which there are more than 
one station show a decided tendency to be mushy 
and weak, and have a wide variation in signal 

strength from moment to moment One cannot 

help speculating what is apt to take place in the 
future. We know that the American public have 
had lots of things put over on them without 
complaint. It is hard to believe that they will be 
willing to stand for the huge joke that it is 
possible to successfully operate more than one 
powerful broadcasting station on a single fre- 
quency without serious interference." 

Another correspondent writes from Wyoming 
to the effect that KOA, Denver, is the principal 
reliance for summer and winter reception of the 
entire state. The Federal Radio Commission has 
ordered that station to cut its power in half after 
seven in the evening. Continuing, he writes: "Prac- 
tically every strong station near the east coast is 
located on the same frequency as some powerful 
station on the west coast. While probably they 
do not interfere in their home territory, the 
heterodyne of the two completely ruins reception 
in the Rocky Mountain region. Before the recent 
changes, we could usually depend on woe, 




HOW VISITORS SEE THE ATWATER KENT FACTORY 



Davenport, and wcco, St. Paul, for WEAF pro 
grams, but have been unable to locate either fo 
a long time." 

Another correspondent .vrites from Ohio tha 
he is located "forty-eight miles air line fron 
WTAM, 102 miles from wWj and 95 miles fron 
WAIU . . . WTAM fades so badlv at night that i 
is worse than useless, wwj is 'crowded to death 
on both sides. There is not one station in thi 
group, or any other station, that can be receive! 
here without heterodyning. Yet the Chairman o 
the Federal Radio Commission reports the dis 
trict very much improved. It is all bunk. Som 
stations must be eliminated." 

INTERNATIONAL CONFERENCE CHANGES 
BROADCASTING BANDS 

'"THE International Radio Telegraph Con 
* ference at this writing is still in session ii 
Washington. Very few of the articles of the nev 
international agreement have yet been adopted 
Some opposition has appeared to the Americai 
proposal that no more spark stations shall b 
licensed and that steps be taken to eliminat 
gradually those in existence with a view to thei 
complete disappearance in 1935. The eliminatioi 
of spark transmitters is proposed largely in thi 
interests of the broadcast listener. 

In the matter of frequency allocations, th< 
amateurs, as usual, have defended their positioi 
with great heat. The Japanese delegation, ii 
particular, was far from cordial in its attitudi 
toward amateurs. The British, French and Ger 
man governments sought lower frequency 
channels for broadcasting in the 1000-, 1300- 
1500- and i8oo-meter regions, in addition to thi 
usual bands in general use. It was finally decide( 
to consolidate these requests for a longer wavi 
broadcasting band of setting aside 1500 to ij5< 
meters (200 to 194 kc.)'for the purpose, provid 
ing about two channels with ten-kc. separation 
At this writing, this band is not yet officially 
approved, but is likely to stand. 

The Committee on frequency allocation, whili 
favorably inclined toward the recommendation: 
of the American delegation for the broadcastinj 
band, does not, at this writing, plan to devoti 
the entire 500- to i 5Oo-kc. region to broadcastinj 
purposes. In the plan announced, it proposes t< 
utilize the lower 200 kc. (i.e. from 130010 ijookc 
or 230 to 200 meters) for both broadcasting anc 
ship stations. This does not mean that the 27; 
American broadcasting stations, now occupyinj 
that part of the band, will have to get off, but i 
is likely that ship interference will develop a 
this end of the broadcasting channels. This movi 
on the part of the International Teiegrapl 
Conference will undoubtedly accentuate stil 
further the need for curtailing the number o 
broadcasting stations on the air in the Unitec 
States. 

BROADCASTING NOTES 

THE National Broadcasting Company and th< 
British Broadcasting Company will cooper 
ate in several short-wave international pro 
grams. In 1924, wjz participated in the first at 
tempt at international broadcasting by relay 
A dance music program from the Savoy Hote 
was radiated from England and intercepted a: 
Houlton, Maine, and from there sent by wire t< 
wjz, in New York. The fading experienced or 
the i6oo-meter wavelength, (187 kc.) upon whicl 
the program was relayed, was sufficient to dis 
courage further attempts along these lines a 
that time. With the development of short-wavt 
transmitters, however, more reliable results ma) 
be expected, f ? f IN A statement of its policj 
on international broadcasting, the British Broad- 
casting Company lays considerable stress upor 
the failures of previous attempts along thes( 



JANUARY, 1928 



BRIEF NEWS ABOUT IMPORTANT RADIO MATTERS 



201 



[lines. It describes an experimental relay of pro- 
i grams for Sidney as barely recognizable; a paral- 
lel attempt to relay Melbourne a few days later 
as a complete silence. It regrets that so much 
emphasis has been laid upon the possibilities of 
international broadcasting and points out that 
considerable development work is necessary be- 
fore we can hope for regular and reliable inter- 
national broadcasting. I I t E. T. SOMERSET 
writes us from Sussex, England, that he enjoys 
WGY, wjz, WLW, WEAF and KDKA on their regular 
broadcasting channels, but American programs 
come in with much greater regularity on the high 
frequencies. 2XAZ, WGY'S short-wave twin is the 
star performer, with KDKA on twenty-six meters 
and ZXAF following. He has also heard with 
great clarity, 2XAH, WRNY and WLW on its short 
wave, and ANH, Radio Malabar, Bendosng, Java, 
on 17.4 meters and last, but not least, 2ME, 
Sidney, Australia. It gave him a particular thrill, 
he writes, to hear the clock striking four A. M. in 
Sidney, when it was still seven p. M., British 
summer time, of the previous night. Mr. Somer- 
set advises American fans to listen for 5 OB, 
Daventry, England, on a frequency of 610 kc. 
with 30 kw. output, and Langenberg, Germany, 
with a 25 kw. output on a frequency of 640 kc. 
Iff SAM PICKARD, who first gained fame in 
radio circles as director of the Department of 
Agriculture Radio Service, has been made Fed- 
eral Radio Commissioner to succeed Henry A. 
Bellows, recently resigned to resume the manage- 
ment of wcco. The Commission loses Mr. Bel- 
lows because the gentlemen of the Congress 
failed to confirm his appointment. He was a use- 
ful and hardworking Commissioner. Mr. Pickard 
is qualified to serve on the Commission because 
of his familiarity with its problems as its former 
secretary. Carl H. Butman now becomes Secre- 
tary of the Commission. He is well known to the 
newspaper fraternity and may be helpful to the 
Commission, not only as an efficient secretary, 
but 'n advising it how to handle its relations with 
the press and the public. I I f " I HAVE come to 
the conclusion that it is not a practical or even a 
theoretical advantage to a broadcaster to sponsor 
a program through any small station. The com- 
panies that are marketing national products can 
use radio advertising to excellent advantage but 
for local companies to broadcast through a small 
local station is not good advertising, in my opin- 
ion. Their efforts are so mediocre in comparison 
with the programs sponsored by the big com- 
panies and transmitted through the high power 
of a well equipped, well operated station, that a 
bad impression is made and no benefit is derived." 
That is the statement, not of a newspaper pub- 
lisher, but of Mr. Robert A. Fox, of Ashland, 
Ohio, who owned and operated station WLPC. 
Realizing that the small station serves little use- 
ful purpose, WLPC requested the Federal Radio 
Commission to cancel its license and its owner 
now states that he wishes "about two hundred 
more stations, now operating, would do the 
same." f I f THE DEPARTMENT OF AGRICULTURE 
Farm Radio Service is being broadcast by 
eighty-nine radio stations in thirty-four states. 
Each of these stations will broadcast one or more 
of the eleven regular farm and household radio 
services prepared and released by the U. S. De- 
partment of Agriculture. Such services as these 
help to sell radio to the farmer. 

NEWS OF THE PATENT FIELD 

I EE DEFOREST won a victory over Edwin 
*- Armstrong in the United States Circuit Court 
of Appeals at Philadelphia, which decided that 
he is the inventor of the regenerative or feed-back 
circuit and the oscillating audion. Since the right 
to use both DeForest and Armstrong patents is 
included in the R. C. A. license, the decision does 



not affect the R. C. A's licensees particularly. 
Certain companies, however, operated under 
licenses granted by Armstrong before his patent 
was acquired by the Westinghouse Company, 
appear, through this decision, to be liable for 
royalties under the DeForest patent. There is 
a possibility that this case may now reach the 
Supreme Court, although that body has the 
power to refuse to consider the matter. ? f f THE 
MACKAY interests announce that the DeForest 
victory places them on an equal footing with the 
Radio Corporation of America in the field of 
wireless communication. They will undertake 
immediate steps to establish short-wave wireless 
systems across the Pacific Ocean and throughout 
the United States, f f J PATENT No. i ,639,042, 
recently issued to Wilford MacFadden of 
Philadelphia and assigned to the Atwater Kent 
Manufacturing Company, describes the use of 
a potentiometer for the stabilization of radio- 
frequency amplifiers. This system was used ex- 
tensively before the neutrodyne systemof stabili- 
zation was developed, f f ? THE DUBILIER 
Condenser Company has notified a number of 
manufacturers of the scope of patents 1,635,1 17, 
1,606,212, and 1,455,141, describing plate- 
current supply devices and power amplifiers. 
Included among prospective defendants under 
these patents are various Radio Corporation 
licensees. One of these patents describes a power 
system comprising rectifiers, filter and choke 
circuits, using a. c. on the filaments; another, a 
two-stage power amplifier with 
alternating current on the fila- 
ments and a C battery used to 
obtain grid bias; plate potential is 
obtained from a thermionic recti- 
fier. 

AMONG THE MANUFACTURERS 

TH E Sonora Phonograph Com- 
pany, manufacturers and dis- 
tributors of phonographs and radio 
sets, the Bidhamson Company, a 
patent holding corporation, organ- 
ized by John Hays Hammond, Jr., 
Lewis Kausman and others, and the 
Premier Laboratories, headed by 
Miller Reese Hutchinson, have 
recently merged to form a corpora- 
tion devoted to the manufacture 
of acoustic devices, f f f ARTHUR 
D. LORD, receiver in equity of the 
DeForest Radio Company, has 
filed a complaint with the Federal 
Trade Commission on Clause IX 
of the R. C. A. license contract. 
This clause specifically forbids 
R. C. A. licensees to equip and 
sell licensed radio sets without 
equipping them with R. C. A. or 
Cunningham tubes to make them 
initially operative. In his com- 
plaint, Mr. Lord claims that the 
consumer is penalized because he 
is forced to take a tube which 
otherwise might not be his choice. 
The clause is obviously aimed at 
independent tube manufacturers. 
He expfesses the belief that this is 
an attempt at monopoly and re- 
straint of trade, a direct violation 
of the Federal Trade Commission 
Act, the Clayton Act and the 
Sherman Anti Trust Law. if "f I 
IN FULL page newspaper advertise- 
ments in the principal newspapers 
of the country, Mr. A. Atwater 
Kent announced a price reduction 
of twenty per cent, in his receiv- 
ing sets. This reduction, says the 



announcement, is made possible by tremendous 
increase in production facilities. Particularly in 
the lower price classes, we may expect an era of 
intensive price competition with consequent ad- 
vantages to theconsumer. I t f POWELCROSLEY, 
JR., has announced that his Bandbox model will 
probably not be changed for several years. This 
is the first time that a manufacturer has ven- 
tured such a prediction, fit THE STEWART 
WARNER Speedometer Corporation, which has 
long defied the R. C. A. in patent matters, is the 
most recent addition to the ranks of those com- 
mitted to a 75 per cent, royalty. 

A STATEMENT by Dr. J. H. Dellinger, 
calls attention to a general current mis- 
understanding regarding short-wave beam com- 
munication. The international short-wave beam 
links confine the radiated energy to a thirty- 
degree arc which is indeed not concentration in a 
single narrow path. It represents merely. Doctor 
Dellinger points out, an economic advantage 
and not a secrecy system. 

Science has been unable to affect a concentra- 
tion of radiated wave energy, either light, sound, 
or heat, in a perfect single beam by the aid of 
any form of reflector, and there seems little 
ground for hope that we shall soon achieve it 
with radio telegraphy or telephony. The concept 
that we may reduce beam transmission to a 
concentration comparable to that obtainable by 
wire communication is now untenable. 




THE NEW COAST GUARD SHORT-WAVE 

TRANSMITTER 

B. J. Fadden, chief radioman aboard the U. S. C. G. Modoc in 
ice patrol duty is shown standing beside the 35.5-meter 
(85oo-kc.) transmitter. The transmitter on this wave is used 
for direct communication between the Modoc while in the 
North Atlantic ice fields and headquarters in Washington 




RADIO BROADCAST Photograph 

MAKING FINAL ADJUSTMENTS ON THE PUSH-PULL AMPLIFIER DESCRIBED IN THIS ARTICLE 

Measurements of the grid bias voltage are being made. Note the electro-dynamic Magnavox loud speaker in the background. A circular baffle- 
board has been attached to it in the laboratory 

PUSH-PULL AMPLIFICATION WHY? 

By HOWARD E. RHODES 



THE essential prerequisites for faithful 
reproduction from a radio set are, first, 
a properly designed receiver capable of 
giving reasonably distortionless amplification 
and, secondly, a good loud speaker fed with 
power from a source able to supply the necessary 
energy without overloading. Much of the dis- 
tortion in receivers is due to tube overloading, 
which usually occurs to the greatest extent in 
the last audio tube. The cure for this condition, 
obviously, is to use a tube, or combination of 
tubes, in the output circuit that has a high 
enough power rating so that over- 
loading will not take place. As will 
be brought out in the following dis- 
cussion, this requires that "power" 
tubes be used in the output circuit 
of the receiver, and at the end of 
the article some constructional de- 
tails will be given regarding a push- 
pull amplifier employing 210 type 
tubes. Such an amplifier will deliver 
a large amount of power to a loud 
speaker without overloading. 

Let us first determine approxi- 
mately what requirements are nec- 
essary in the output of a receiver 
to prevent serious overloading. By 
the term "overloading," in this dis- 
cussion, we mean that the input 
voltage on the grid of the tube is 
so great as to cause the grid to be- 
come positive at times so that cur- 
rent begins to flow in the grid circuit. 
In the operation of any ordinary 
amplifier, care must be taken that 
the signal input voltage is never 
great enough to cause grid current to 
flow for, when this does occur, the 



input signal will be badly distorted. In deter- 
mining the characteristics of an amplifier to pre- 
vent overloading, we must assume certain values, 
with the result that the final answer will not be 
exact, but should nevertheless give a good idea 
of what conditions must be met. Suppose, to 
take an average case, that an orchestra is 
broadcasting and that the ratio of power be- 
tween the fortissimo and pianissimo passages as 
played by the orchestra, is a million to one, 
corresponding to a power ratio of 60 TU. Be- 
cause of the characteristics of the amplifier 




RAD.O BODCASI Photograph 

A CLOSE UP 

Showing the plug which provides for variations in line voltage 
2O2 



used to pick up this music, it is necessary to 
cut down this power ratio somewhat so as to 
keep the pianissimo passages above the noise 
level and to prevent the fortissimo passages 
from overloading the amplifier. In practice, 
this ratio is cut down in the control room at the 
broadcasting station by an operator in charge of 
the gain control. The power ratio is, after being 
cut down, generally about 40 TU into the 
amplifier system. This corresponds to a ratio 
of ten thousand to one. Let us assume that this 
ratio is maintained throughout the entire broad- 
casting and receiving system, a con- 
dition which will be true if there 
is no overloading at any point. Sup- 
pose that the energy in the pianis- 
simo passages as they are reproduced 
by the loud speaker is 3 microwatts 
(0.000003 watts). 

I o get an idea of what this 
amount of energy represents, it may 
be compared to the average speech 
power delivered by a person speak- 
ing, which is about 10 microwatts. 
The energy associated with the 
fortissimo passages will be 10,000 
times as great, or 0.03 watt. It is 
now necessary to assume a figure 
for the average efficiency of the 
loud speaker, but because the effi- 
ciency of a loud speaker varies con- 
siderably over the range of audio 
frequencies, it is hardly accurate to 
assume an average efficiency and 
have it mean very much. We wilt 
do so in this case, however, merely to 
get some idea of how much power is 
required. The efficiency of a loud 
speaker is very low, we will assume 



f 



JANUARY, 1928 



PUSH-PULL AMPLIFICATION WHY? 



203 



it to be 3 per cent., which means that, in order 
to obtain a given amount of sound energy, we 
must supply the loud speaker with many times as 
much electrical energy. The amount of electrical 
energy required is found by dividing the sound 
energy output by the efficiency of the loud 
speaker; in this case we must divide 0.03 watt 
by 0.03 (3 per cent.) and the quotient, one 
watt, is the amount of energy the power tube 
in the receiver must be capable of delivering to 
the loud speaker during the fortissimo passages. 
Now let us see what tube or combination of 
tubes is capable of supplying this power. 

The maximum amount of undistorted power 
that can be obtained from various tubes is 
given below. 

TABLE NO. i 



PARALLEL 
ARRANGEMENT 

(i.) Requires only half as 
much input foliage from 
receiver to give same out- 
put as push-pull ar- 
rangement. 

(2.) Distortion due to over- 
load quite noticeable. 

(3.) Voltage gain somewhat 
higher. 

(4.) Plate Impedance four 
times smaller than push- 
pull arrangement. 

(5.) Distortion due to cur- 
vature of tube charac- 
teristic not eliminated. 

(6.) Some hum may result 
if filaments are oper- 
ated on a. c. 



PUSH-PULL 
ARRANGEMENT 

Requires twice as much 
input voltage from receiver 
to give same output power 
as parallel arrangement. 

Slight overload (about 25 
per cent.) possible without 
noticeable distortion. 
Voltage gain is somewhat 
lower. 

Plate impedance four times 
greater than parallel ar- 
rangement. 

Distortion due to curvature 
of tube characteristic elim- 
inated. 

Any a. c. bum from fila- 
ments eliminated due to push- 
pull arrangement 



TABLE NO. 2 



OUTPUT 
RESISTANCE 


INCREASE 
IN CURRENT 


DECREASE 
IN CURRENT 


10,000 
5,000 
1,000 


5 
7 
'4 


I 
1 1 



TUBE 
TYPE 


PLATE 
VOLTAGE 


GRID 
VOLTAGE 


UNDISTORTED 
OUTPUT 
WATTS 


'99 


90 


- 4-5 


0.007 


1 20 


'35 


-22.5 


0. 1 IO 


2O I -A 


90 


-90 


0.055 


112 


"57 


-10.5 


0.195 


171 


180 


-40.5 


0.700 


2IO 


450 


-38 


i .700 



We shall endeavor to explain now how the push- 
pull amplifier eliminates a certain type of dis- 
tortion which exists in a simple single-tube am- 
plifier. It is necessary to start the discussion by 
examining in some detail the characteristics of a 
cx-3io (ux-2io) type tube (or, for that matter, 
any tube). 



When two tubes are used in a push-pull ar- 
rangement the maximum power output of the 
combination is twice that of a single tube. 

It is evident from the table that 
the only tubes delivering, in push- 
pull arrangement, more than I watt 
of power are the 171 and 210 com- 
binations, and, therefore, these com- 
binations are most satisfactory for 
supplying a loud speaker with the 
necessary amount of undistorted 
power. In practice it will be found 
that a push-pull amplifier can be 
overloaded, but this amount of 
overload is so small as to be negligible. 

This treatment of the problem is not exact. 
It was necessary to assume an average value for 
the power associated with the pianissimo pas- 
sages and this first assumption determines how 
much power will be required for the fortissimo 
passages. It is also true that a considerable 
amount of distortion can be present in the 
output of a loud speaker without being evident 
to most of us. The figures do, nevertheless, give 
an idea of why power tubes must be used, and 
show that present-day loud speakers cannot 
be supplied with sufficient undistorted power 
from tubes other than the 171 or 210 type. 
Marked improvement in the efficiency of loud 
speakers will some day make other tubes with 
a lower power output suitable for use in the last 
stage of a receiver, but until such an improve- 
ment is made, we must make certain that we 
have plenty of power handling capacity avail- 
able in the receiver's output. 

PUSH-PULL OR PARALLEL TUBES? 

A T THIS point there might be some question 
"* regarding the relative merits of a push- 
pull amplifier with two 210 tubes and a parallel 
arrangement of the same tubes. Let us list the 
advantages and disadvantages of the two ar- 
rangements. 

The italics indicate with which arrangement 
the advantage lies. Although point No. 4 was 
indicated as an advantage for the parallel ar- 
rangement, it is possible, by the use of a special 
push-pull output transformer, to compensate the 
higher plate impedance of the push-pull circuit, 
and the two arrangements will then be equal 
in this respect. Point No. 5 has not, as yet, been 
explained, but it is the most important reason 
for the existence of the push-pull arrangement: 




FIG. I 
Grid voltage -plate current curves of a 210 type tube 

In Fig. i we have drawn several curves for a 
single tube of the 210 type with a plate voltage 
of 400 and a grid bias of -35 volts, and these 
curves show the relation between the plate cur- 
rent and the grid voltage with various load 
resistances in the plate circuit. The curve marked 
1000 was made with a looo-ohm resistance in 
the plate circuit and the curves marked 5000 and 
10,000 were made with resistances of 5000 and 
10,000 ohms respectively in the plate circuits. 
These curves are dynamic characteristics in the 
sense that they indicate how the plate current 
will vary with different loads in the plate circuit. 
If a signal having a value of, for example, 10 
volts, is impressed on the grid of this tube, it 
will cause the grid voltage to vary 10 volts either 
side of its average value of 35 volts. Such a sig- 
nal voltage is represented in Fig. I by the curve, 
marked "signal voltage," drawn below the grid 
voltage axis. If the change in plate current due 
to this voltage is determined on the io,ooo-ohm 
curve by reading the values of plate current at 
each extremity, we find that, when the voltage 
is positive, 'the current rises to 21 milliamperes 
and that, when the voltage is negative, the cur- 
rent decreases to 1 1 milliamperes, a drop of 10 
milliamperes. 

The signal voltage of 10 volts has, therefore, 
caused the plate current to increase and decrease 
an equal amount with respect to the average 
value, the increase and decrease being 5-milli- 
amperes in this case. If the same measurements 
are made on the 500o-ohm curve we find that 
the plate current increases 7 milliamperes above 
the average value but only decreases 6 milli- 
amperes. On the looo-ohm curve the increase is 
14 milliamperes and the decrease is only 11 
milliamperes. These values have been arranged 
in the form of a table: 



This table indicates clearly that, as the resist- 
ance in the output circuit of the tube decreases, 
the increase and decrease in plate current due 
to a given signal become unequal. This represents 
distortion because it indicates that the positive 
side of the input voltage produces a relatively 
greater change in the plate current than does 
the negative side. 

100 LOUD SPEAKER CONSIDERATIONS 

AND now let us consider the 
^* loud speaker. The impedance of 
a loud speaker is a function of fre- 
quency and increases with increase 
in frequency. At low frequencies, 
therefore, the loud speaker will have 
a comparatively low impedance and 
the tube feeding the loud speaker 
will then operate on the character- 
istic corresponding to a low-resist- 
ance load in the plate circuit. This 
characteristic is indicated by the 
looo-ohm curve in Fig. i. At me- 
dium frequencies, where the loud 
speaker's impedance is higher, the 
tube will operate on a characteristic 
similar to the 5OOO-ohm curve, and 
at high frequencies the tube will 
operate on a characteristic similar 
to the io,ooo-ohm curve. As in- 
dicated by the figures in table No. 2, 
the io,ooo-ohm curve is quite 
straight and therefore produces 
little distortion. A small amount of distortion is 
produced by the 5OOO-ohm curve, but much 
greater distortion occurs when the tube operates 
along the jooo-ohm curve. When a loud speaker 
is operated from a single 210 type tube, this dis- 
tortion occurs and, if possible, it would evi- 
dently be of advantage to arrange the circuit 
so that no distortion of this type is produced. 
This leads us to consider push-pull amplifica- 
tion. 

The circuit diagram of a push-pull amplifiei 
is given in Fig. 2. In some push-pull arrange- 
ments the output choke, L, is replaced by a 
transformer, but the circuit will function with 
a simple choke coil as indicated. When a signal 
is induced in the secondary of the input trans- 
former, T, the voltage relations are as indicated 
by the plus and minus signs on the diagram. It 
will be noted that the voltage at one end of the 
transformer is positive relative to the. voltage 
at the other end, which is negative. The signal 
voltage impressed on either grid is one half the 
total voltage across the transformer. Since the 
two grids are at relatively opposite potential 
the plate current changes will also be opposite 



Input 




Speaker 



FIG. 2 
The circuit connections for a push-pull amplifier 



204 



RADIO BROADCAST 



JANUARY, 1928 



in nature. Referring to Fig. I, this means that, 
during the time that the grid of tube No. 2 goes 
positive, the plate current will increase, and that 
the plate current of No. 2, as the grid goes 
negative, will decrease. In Fig. 3, we have 
represented at A the signal induced in the 
secondary of the input transformer, T, curve A-i 
indicating how the voltage on the grid of tube 
No. i varies and curve A-2 indicating the vari- 
ation of voltage on the grid of tube No. 2. It 
should he noted that the voltages are similar, 
that there is no distortion, and that the voltages 
are in opposite phase relation to each other 
(when one is positive the other is negative). 
Now these voltages cause changes in plate cur- 
rent in accordance with the curves given in Fig. 
I, and if the particular signal being amplified is 
low in frequency, the loud speaker's impedance 
will be low and the tube's characteristic will have 
a form similar to the looo-ohm curve. This 
curve will produce unequal changes in plate cur- 
rent (see table No. 2) and the curves at B-i 
and B-2 in Fig. 3 indicate the change in plate 
current due to the voltages impressed on the 
grid. It should be noted that these two curves 
are distorted (the positive halves are larger 
than the negative halves) although the distor- 
tion of the two curves is similar in nature. 
These curves at B can be split into two parts, 
as indicated at C, C-i and C-2 represent plate 
current variations exactly similar in form to 
the grid voltage variations and C-j and C-4 
represent additional plate current variations 
due to the curvature of the tube characteristic. 
The point of interest here is that, although the 
variations in plate current indicated by C-i and 
C-2 are out of phase (as they should be) the dis- 
torted parts represented by C-3 and C-4 are in 
phase; that is, they are both positive or negative 
at the same time. In order to have current flow 
through the loud speaker, the a. c. voltage at one 
plate must be opposite in sign relative to the 
voltage at the other plate. We might consider 
that the plate whose voltage is negative tries to 
"pull" some current through the loud speaker 
while the plate whose voltage is positive tries 
to "push" some current through the loud 
speaker, and this gives us an idea of why such 
an amplifier is termed ''push-pull." C-} and C-4, 
indicating the distorted part of the plate cur- 






-C-3 





FIG. 3 
These curves are used to explain how a push-pull amplifier operates 



rent variation produced by the curvature of the 
tube characteristic, are such that both plates 
are relatively positive at the same time. These 
currents, therefore, cannot force any energy 
through the loud speaker. The only current 
flowing through the loud speaker is indicated by 
C-i and C-2, and it is undistorted. In this way 
two tubes in a push-pull arrangement eliminate 



Gain 





5 10 15 20 25 30 35 40 

VOLTS ACROSS PRI. OF INPUT TRANSFORMER 

FIG. 4 

What happens when an amplifier is overloaded 

can be determined from these curves. They are 

explained in the text, col. 3, page 204 




RADIO BROADCAST Photograph 
THE LAYOUT OF THE PUSH-PULL AMPLIFIER FROM ABOVE 

Nod. c. plate current can flow through the loud speaker, and blocking condensers are therefore 
not necessary in this amplifier for this purpose. However, in the arrangement shown the loud speaker 
itself is at a potential of 500 volts above ground and a serious shock will be had if the loud speaker 
and a grounded object are touched at the same time. In order to make the installation entirely safe 
it is a good idea to connect a 4-mfd. high-voltage condenser in series with each lead to the loud 

speaker terminals 



a form of distortion present in a simple circuit 
using a single tube. 

In Fig. 4 are given a group of curves obtained 
from some data on the Samson push-pull ampli- 
fier illustrated in this article. The three curves 
shown in solid lines were made using a single 
210 type tube. Note how the gain begins to fall 
off when the voltage on the grid reaches about 
18 volts and this point also corresponds approxi- 
mately to the point at which grid current begins 
to flow. The power output also begins to flatten 
out after more than 18 volts is placed across the 
input. These three effects, a decrease in the gain, 
the presence of grid current, and a falling off in 
power output, are all definite indications of over- 
loading. The dotted curve indicates the power 
output obtained from two 2io's in a push-pull 
amplifier. This curve also begins to fall off 
slightly after about 18 volts has been placed on 
the input, but the change is not as rapid as in 
the case of a single tube. The power output of 
the push-pull amplifier at the point where grid 
current begins to flow is twice as great as that 01 
a single tube. 

The Samson push-pull amplifier illustrated 
in this article is an excellent example of a well- 
designed unit. The major characteristics of this 
amplifier are as follows: 

(i.) The unit consists of two 210 type tubes in 
a push-pull arrangement fed from an input 
push-pull transformer. The unit is designed 
to connect to the output of the first audio 
stage in a receiver, and thereby makes pos- 
sible the attainment of better quality than 
can be obtained from the smaller tubes or- 
dinarily used in a receiver. 

(2.) The power transformer and choke coils have 
been enclosed in a nicely finished metal 
case with the various leads brought out 
through a small terminal box at one end. 
At the other end of the transformer is a 
special plug, a Samson feature, which can 
be turned to different points to compensate 
differences in line voltage. The condenser 
bank is also enclosed in a metal case. 

(3.) The device will supply B power to a re- 
ceiver. The circuit incorporates a glow 
tube which maintains the output voltages 
from the various terminals practically con- 
stant independent of load, and this makes 
it possible to use the device with almost 
any receiver with assurance that the vol- 
tages marked on the terminals will be equal 
to the actual voltages delivered by the de- 
vice. The following voltages are available; 
180, 135, go, 6y|, and a variable tap so that 
accurate adjustment of the detector voltage 
can be made. The 210 type tubes receive 
about 500 volts and the C bias is about 40 
volts. The device also supplies C potentials 
as follows: -4.5, -9, and -43. 

The circuit diagram of this power amplifier is 
given in Fig. 5. The following parts were used 
in the amplifier illustrated in this article. 



JANUARY, 1928 



PUSH-PULL AMPLIFICATION WHY? 



205 



LISTS OF PARTS 

TL Samson Power Block, Type 210, 

Containing Power Transformer and . 

Two Filter Choke Coils . . . . f 37.00 

Tobe Condenser Block, for Samson 
Power Amplifier, Containing the 
Eleven Necessary Condensers . . 38.00 

R; Electrad y2oo-Ohm Type C "Tru- 
Volt" Resistance, 50 Watts . . . 2.25 

Ro Electrad 42o-Ohm Type C "Tru- 
Volt" Resistance, 25 Watts . . . 1.50 

R, Electrad 5O,ooo-Ohm Variable 

Resistance, Type T-joo .... 3.50 

R< Tobe io,ooo-Ohm Veritas Resist- 
ance 1.10 

T Samson Input Push-PuII Trans- \ 
former, Type Y ( 

Lr- Samson Output Push-PuII Choke, ( 
TypeZ J 

12 Eby Binding Posts .... 1. 80 

4 Benjamin Sockets 3.00 

2 RCA ux-2io (Cunningham cx- 
310) Tubes 18.00 



i RCA ux-8y4 (Cunningham cx- 

376) Tube 5.50 

i RCA ux-28i (Cunningham cx- 

381) Tube 7.50 



TOTAL 



$138.65 



The circuit diagram has been marked with 
figures corresponding to the terminal markings 
on the power block and the condenser block. 
The arrangement of the apparatus on a single 
large baseboard makes it a simple matter to 
construct it and the circuit diagrams and pho- 
tographs given herewith should supply all the 
necessary information. 

All of the transformer cases, and also the 
case of the condenser block, should be con- 
nected to the negative B, as indicated in the 
schematic diagram, to prevent hum. This 
grounding can generally be most readily accom- 
plished by running a lead from the negative B 
to the mounting screws of the various units. 
The wire can be fastened under these mount- 
ing screws. Remember that the voltages de- 



livered by the transformer are very high and 
therefore care is necessary in making all of 
the connections. The 5O,ooo-ohm resistance is 
the only variable control in the entire unit, and 
it is used to obtain accurate adjustment of the 
detector voltages. 

When the construction has been completed, 
the special plug on the power input side of the 
Samson transformer may be inserted in the 
correct manner and connected to the a.c. light 
socket. When this is done, the tubes should 
light and the regulator tube should glow with 
a pinkish light. 

In operation, the transformer block may be- 
come somewhat warm, but if it becomes so hot 
that the hand cannot be comfortably held on it, 
it indicates some error in the wiring. The input 
terminals of the device should be connected to 
the output of the first stage of the receiver and 
the loud speaker then be connected to the out- 
put of the amplifier. 

If carefully constructed and properly operated, 
the unit will be found capable of giving excel- 
lent reproduction. 






Caution: Ground here only 
if A Battery is not groundec 




180V O 
135 v.O 



-4.5V. O 



-43V. O 



F- F+ 
874 Regulator 
Tube Connections 



FIG. 5 

This is a complete circuit diagram of the Samson push-pull power 
amplifier. The various numerals on the units correspond with 
the markings on the terminal blocks on the various parts; num- 
bers in circles indicate terminals on the condenser block. This 
amplifier employs two 210 type tubes in the push-pull circuit, a 
type 281 tube as the rectifier, and an 874 type regulator tube. 
The connections to the socket holding the latter tube are indicated 
in the diagram. The P and F minus terminals on the socket 
are connected in the filter circuit as shown at the point marked 
"874 BK." on the diagram. The two corresponding contacts on the 
tube are short-circuited inside of the tube base during the process 
of manufacture and, therefore, if the regulator tube is removed 
from its socket while the power is on, the circuit is automatically 
opened and damage to the filter condensers thus prevented. The G 
post on the socket connects to the + go voltage tap and the 
F + terminal connects to B minus 



Condensers 
Mounted in 
One Block 



TTTTTTT 



R 



-1500V. O.C. '~-400V.D.C. 
C BLOCK 




-200V.D.C. 



'/ T O JUDGE by the sale of radio-phonograph 
-* combination instruments and the popularity of 
the various electromagnetic pick-up units, the 
phonograph and the radio set in combination are 
climbing to high favor among radio users. If you 
have a good radio receiver and loud speaker, the 
purchase of a magnetic pick-up makes your old 
phonograph up to dale and all the fine new electrical 
recordings then pour out of your loud speaker 
sounding as well as the best radio program. This 
magazine and others have contained descriptions on 
how to bring the old phonograph up to date using the 
electromagnetic pick-up. These pages on the enter- 
tainment that the radio-phonograph offers to the 
user are a regular feature of RADIO BROADCAST. 
It is not enough to know that the combination of the 
radio and phonograph provides a flexibility of home 
entertainment that is astounding we feel our 
readers would also like to know what the disks 
actually offer. These columns discuss only the 
records made by artists well known to broadcasting. 

THE EDITOR. 



A New Use for Records 

TN THE days when life was simpler, we thought 
of the phonograph merely as an instrument 
for the diversion of the multitude of home-loving 
folk, who were enabled by it to listen to jazz or 
classical music without budging an inch from 
their Franklin stoves. Then someone realized 
that by preserving on its records the speeches, 
music and other audible accompaniments of 
events of national importance the phonograph 
could be made to have a definite historical im- 
portance. And now the phonograph has had 
another burden laid upon it, that of delivering 
speeches for important individuals at gatherings 
at which they cannot themselves be present. 
This was actually done at the opening of the fifth 
annual convention of the American Institute of 
Steel Construction in Pinehurst, North Carolina, 
on October 25. Secretary of Commerce Herbert 
Hoover was asked to deliver the speech of wel- 



The PHONOGRAPH 




A CLOSE-UP OF VICTORS NO. 955 
" ELECTROLA" 

This illustration shows the radio panel of this 
elaborate combination radio phonograph model. 
The radio panel can be tipped for convenience in 
operation as shown here, or it can be tilted up- 
right. Pilot lights make tuning easy. This instru- 
ment, completely electrically operated will play 
12 records without stopping, contains built-in 
loop, power loud speaker (shown behind the grille 
above) and power supply. Price complete, $1550 



come at this convention, but he could not take 
the time to make the trip there and back. The 
Institute, determined to have the speech, en- 
listed the services of the Victor Company, who 
made a record of a speech which Mr. Hoover 
delivered in his own office in Washington, and on 
October 25 this record was reproduced in Pine- 
hurst before the convention. As Mr. Hoover 
himself remarked, one of the advantages of this 
method is that it puts a definite time limit on 
speeches. What a unique device for curtailing 
long-winded recitations! And what a splendid way 
to eliminate superfluous oratory, for as the Secre- 
tary also noted, and as all who have broadcast 
well know, a microphone is about as inspiring 
an audience as a bathroom door knob! We 
foresee a great future for this branch of phono- 
graph service. 

A Review of Recent Records 

BUT though the phonograph now has a Mis- 
sion it still continues to provide amusement 
and entertainment for those who want it. And, as 
far as we can see, the recent output of records is 
much the same as ever; there are many good 
records, a few poor ones, and a goodly supply 
of in-betweens. Of the latter the majority seem 
to be instrumental dance records. The orchestras 
which play for these are admirable and the record- 
ing of their playing is in most cases all it should 
be, but the selections on which they waste their 
talent are just about zero in musical worth. The 
result is like apple pie without the apple. Alas 
for more Gershwins and Berlins! 

On the Victor, Columbia and Brunswick lists 
are many names familiar to those who sat at 
home turning the dials of their radio sets through 
the long winter evenings of 1926-27. They will 
recognize numerous regular performers and 
others who have made only a limited number of 
ethereal bows on such programs as Atwater Kent, 
Eveready, and Victor. New names are being 
added daily to this register of recording-broad- 
casters and now that Columbia has its aerial 
chain, we can expect even more. 

Of the recent dance records, Who Do You Love? 
and /'// Always Remember You played by Paul 
Whiteman and His Orchestra (Victor) head the 
list. This famed outfit have taken two of the best 
songs now extant and by decorating them with a 
trick orchestration in the inimitable Whiteman 
manner have made an unusually good record out 
of them. 

Is It Possible? and Just Call On Me played by 
Leo Reisman and his Orchestra (Columbia) is 
another grand record. If we hadn't always lived 
in the belief that Whiteman had no equal, we 
would say this was as good as the first record on 
our list. We will say it. Anyway, it is pretty 
smooth music and we defy you to keep your feet 
still when you listen to either number. 

Gorgeous by Johnny Hamp's Kentucky 
Serenaders would be an asset to any collection of 
dance records and its companion on the opposite 
side, There's a Trick in Pickin a Cbick-Cbick- 



THE UTICA JUBILEE SINGERS 
There are those who are not especially impressed 
by negro spirituals. But if you like these interest- 
ing melodies and want to hear them sung as they 
should be sung, listen to this group on wjz and 
associated stations at 9:45 eastern time Sunday 
evenings. They have made one double-faced 
recording for Victor, one of the finest recordings 
of the kind we have heard 

206 



Chicken by Nat Shilkret and His Vic-Vic-Victor 
Orchestra is just as full of pep. (Victor). 

Habitual listeners-in on Harold Leonard and 
his Waldorf Astoria Orchestra will want his 
latest Columbia product, Just A Memory and 
Joy Bells. You don't have to be told it is good. 

Once Again and No Wonder I'm Happy 
as played by Ernie Golden and his Hotel Mc- 
Alpin Orchestra will have the ring of familiarity 
to those who tune-in on station WMCA. They are 
good snappy numbers. (Brunswick.) 

Having heard excellent reports of the new 
Broadway show "Good News" we were disap- 
pointed in the three numbers from it which have 
found their way onto the rubber discs. The title 
number, Good News, and Lucky in Love have been 
recorded for Columbia by Fred Rich and his 
Hotel Astor Orchestra, and Cass Hagan and his 
Park Central Hotel Orchestra have done The 
Varsity Drag (also Columbia). If you are one of 
those who raved over the show you may enjoy 
the records. You may also like Dancing Tam- 
bourine by the Radiolites on the reverse side of 
The Varsity Drag, though we can't enthuse over it. 
If you stuff cotton in your ears during the 
seconds devoted to the vocal chorus in Baby Feet 
Go Fitter Patter you may agree with us that this 
record by Abe Lyman's California Orchestra 
(Brunswick) is one of the best that have appeared 
in many moons. In addition to an aversion to 
vocal choruses in general we detest the words to 
this particular song. It was an error on someone's 
part to attach such a silly lyric to such an excel- 
lent tune. However, it's short and the few seconds 
one sacrifices to get through it are a drop in the 
bucket and the rest of the record is fine. The other 
side carries There's One Little Girl Who Loves Me, 
also played by Abe Lyman, and also good. 

Another of the better records slightly marred 
by a vocal chorus is No Wonder I'm Happy and 
Sing Me a Baby Song by the George H. Green 
Trio with Vaughn De Leath doing the vocalizing. 
(Columbia.) 

The Ipana Troubadours, smile vendors under 
the direction of S. C. Lanin, have done a fine 
job with Are You Happy? and A Night in June, 
of which Frank Harris carols the chorus. (Colum- 
bia.) 

Inhabitants of Mayor Thompson's Strictly 
American City will welcome a Columbia disk 
made by one of Chicago's Municipal Heroes, 
Paul Ash, and his Orchestra. Just Once Again 
is excellent and its vocal chorus by Franklin 
Baur makes us eat some of our words just 
uttered; we must admit it is an addition to the 




Joins the RADIO Set 



record. In self-justification we insist that Frank- 
lin Baur is an exception. The reverse of the record 
Lone and Kisses, is not quite up to the Paul Ash 
standard but that doesn't mean it is bad. 

Several other records get only half a vote due 
to the fact that one face of record is good and 
the other not. Stop, Go ! executed by Nat Shil- 
kret and the Victor Orchestra has a unique 
rhythm, better than any other number on the 
list but Something To Tell is only moderate. 
Me and My Shadow by Phil Ohman and Victor 
Arden and their Orchestra is good; Broken 
Hearted is not. Even Paul Whiteman could not 
do much better with that last number but 
Collette on the reverse makes the record decidedly 
worth buying. (Victor). Don Voorhees tried some- 
thing tricky with Soliloquy (which we are told 
belongs to the new school of music ushered in 
by the Rhapsody in Blue) and was not very suc- 
cessful, but his more orthodox My Blue Heaven 
is exceedingly good. Just a Little Cuter falls rather 
flat but Marionette is excellent dance music. 
Both come from the orchestra under the baton 
of Ben Selvin and are recorded by Brunswick. 

We dont care much for Cheerie Beerie Be or 
Waters of the Perkiomen even though played by 
Leo Reisman and his Orchestra. Roodles and / 
Ain'l Got Nobody are not as good as they ought to 
be coming as they do from Coon-Sanders Orches- 
tra. And we were very much disappointed in 
Who's That Pretty Baby? and Barbara by Paul 
Specht and his Orchestra. The fault lies in each 
case not with the orchestras but with the stupid 
selections they play. 

AND NOW FOR COMEDY 

OF THE good humorous records recently is- 
sued by far the best is Two Black Crows, 
Parts 3 and 4. (Columbia). Of course we don't 
need to describe it. Everyone knows Moran and 
Mack and their riotously funny dialogues. What, 
you dont? Well, go right down to the corner 
music store and buy this record and their first 
one, Two Black Crows, Parts i and 2. You will 
remember us in your prayers. 

Next in order of importance comes that grand 
song perpetrated by the Happiness Boys, Billy 
Jones and Ernest Hare, Since Henry Ford Apolo- 
gi^ed To Me. (Victor.) It is worth seventy-five 
cents just to hear this record once, which is fortu- 
nate, for we wouldn't give a nickel for the song on 
the reverse side, / Walked Back From The Buggy 
Ride, by Vaughn De Leath and Frank Harris. 

Then the famous Sam and Henry combination 
(Correll and Gosden of WGN) offer two dialogues 
called Sam's Big Night and The Morning After. 
(Victor.) They are both labelled comic dialogues 




but oh! the pathos of Sam's refrain, "Henry, 
Henry, I'se sick! My head's bout to kill me! ... I 
b'lieve I'se gonna die!" It almost makes you want 
to sign the pledge. 

Of the many popular vocal records we nomi- 
nate for first place, a work of art by the Happiness 
Boys, You Dont Like It Not Much and Oh Ja Ja. 
(Victor.) This is typical of what they offer to the 
audience of WEAF every Friday night and it's 
good! Personally we like them best of all the 
regular aerial performers, It's personality that 
does it plus good voices. 

Van and Schenck sing Magnolia and Pasta- 
fa^oola for you on a Columbia record. The Radio 
Franks present No Wonder I'm Happy and When 
Day Is Done. (Brunswick). And Johnny Marvin 
and Ed Smalle do a little duet with Just Another 
Day Wasted Away on a Victor. Ml of these are 
good. But on the back of the last mentioned disk 
is Just Like a Butterfly sung by Franklyn Baur. 
Personally, as little Alice said in Peggy Ann, we'd 
rather have a baked apple. No matter how good 
the voice, the song is terrible! We feel just as 
strongly about Baby Feet Go Fitter Patter as we 
have hinted before, and when it is sung by 
Vaughn De Leath we see spots before our eyes. 
She could make Turkey in the Straw sound like a 
sentimental ditty and when she has something 
as mawkish as this to start with . . . words fail us. 
In case you are still interested in the record the 
opposite side bears another song by the same 
lady, Sometimes I'm Happy (Brunswick). 

The Sunflower Girl of WBAP vocalizes You 
Went Away Too Far and / Hold The World in 
The Palm of My Hand on a Columbia disk. We 
cannot say she sings them because she has one 
of those rough and tumble shouts so often heard 
on the vaudeville stage. It is about as far from 
being musical as anything could be, but for that 
sort of thing, she will do. 

We don't feel strongly one way or another 
about Charmaine! and The Far-Away Bells sung 
by Franklyn Baur (Columbia), Ain't That a 
Grand and Glorious Feeling? and Magnolia, sung 
by Harry Richman (Brunswick), or Flutter By, 
Butterfly and I'd Walk a Million Miles by Art 
Gillham and his Southland Syncopators (Colum- 
bia). 

RED SEAL RECORDS AND SUCH 

TURNING now to the sublime we find several 
red seal records made by operatic stars from 
the Metropolitan firmament, who twinkled be- 
fore microphones upon occasion last winter, 
Lucrezia Bori, the beautiful Spanish soprano 
who is as lovely to look upon as she is to listen to 
(though you couldn't tell that when you heard 
her sing in the Victor radio concerts or in the 
Atwater Kent hour) presents us with the lovely 
old waltz song by Pestalozza, Ciribiribin, and 
// Bacio by Ardit. (Victor). 

Another soprano who was presented to the 
radio audience by Atwater Kent is Hulda 
Lashanska In company with Paul Reimers, 
tenor, she records for Victor two simple but ex- 
tremely lovely old German folk songs, Du, Du 
Liegst Mir Im Her^en and Ach, Wie I si's Moglich 
Dann. The harmony of the first selection is par- 
ticularly notable. 



It was a Victor hour that launched Emilio De 
Gogorza's baritone voice on the ether waves and 
it is a Victor record which presents his voice 
again for your permanent enjoyment. He sings 
two favorites, Sole Mio, and Santa Lucia. 
We think it would be a grand idea for everybody 
to have this record in his home, if for no other 
reason than just so that whenever he hears the 
song murdered by a would-be artist he can play 
the record on the phonograph and reassure him- _ 
self that the song is all right after all. 

We presume it is rank heresy to say that we 
prefer to hear the Utica Jubilee Singers sing 
Old Black Joe than to hear Lawrence Tibbett. 
Tibbett's voice is marvelous, of course, and it is 
perfectly trained, but he cannot manage this 
negro melody as expressively as the Utica Jubilee 
Singers do. If this be treason. . . . The reverse of 
the record is Uncle Ned. We have never heard 
the Jubileers sing this but we will wager our two 
cents that they could do it more to our satis- 
faction than the Metropolitan star has done. 
Both these songs are so worn out that they need 
all the expression that can be put into them. 

The Utica Jubilee Singers have done a record 
for Victor, Angels Watching Over Me and Climbin' 
Up the Mountain. It's perfect! We can say no 
more. Incidentally it is interesting to note that 
these singers have just returned from a concert 
tour of Europe where they were greeted with 
great acclaim, so their popularity is no longer 
limited to this continent. They are now heard 
from wjz and others on that chain Sunday nights 
at 9:45, eastern time. 

Virginia Rea, staff artist for Eveready, has 
recorded a popular number which Victor thought 
good enough for a red seal record, Indian Love 
Call from Rose-Marie; and Lambert Murphy, 
whom you undoubtedly heard in an Atwater 
Kent hour, has recorded the title number from 
the same musical play on the reverse of the rec- 
ord. Though we saw this show at regular in- 
tervals through the winter of 1924-25 and heard 
these numbers on hand organs for the next two 
winters, we still like them. 




ERNIE GOLDEN OF WMCA 

He leads the Hotel McAlpin Orchestra, regularly 

heard through WMCA of New York. The Hotel 

McAlpin Orchestra has recorded many good 

dance numbers for Brunswick 

207 



AN ELECTRIC RADIO-PHONOGRAPH FROM 

FRESHMAN 

This instrument, completely a. c. operated pro- 
vides the usual Freshman receiver, electric turn- 
table, electric pick-up, record space and loud 
speaker which serves for radio or phonograph 
music. Complete with a. c. tubes. $350 



UX-222 TUBES 

Some idea of the con- 
struction of the new 
R. C. A. screened grid 
tube may be obtained 
from this illustration 
The extra connection 
is made to the metal 
cap atop the tube. Eby 
new type sockets are 
shown 




ITT T 

JLU 



STUDENTS of the characteristics and ap- 
plications of the vacuum tube, and of 
circuits to do with it, may find them- 
selves somewhat bewildered by the apparent 
complexity of the screened grid tube when they 
begin their researches into its idiosyncrasies. 
They will be impressed at once with the thought 
that this tube is no ordinary structure, and will 
appreciate more such names as Schottky of 
Germany and Hull of the United States names 
actively associated in its development. Experi- 
menters here have yet to become familiar with 
the new tube, which has already taken its share 
of space in English, French, and German radio 
periodicals, and it is certain that, with the Radio 
Corporation's announcement of the ux-222, not a 




FIG. I 

The plate current of a screened grid tube varies in 
strange fashion, as these curves show. In these 
data the effect upon the plate current of changing 
the plate voltage, with several values of bias 
voltage, is given. The normal bias is about 1.5 
volts, with 45 volts positive on the screen, and 
about 135 on the plate 



By KEITH HENNEY 

Director of the Laboratory 

great length of time will elapse before it will be 
possible for anyone to obtain these interesting 
and useful screened grid tubes. 

American writers, too, will have considerable 
to say about the double-grid tube, of which the 
screened grid tube is a type, as they become 
more familiar with its operation, and as its pos- 
sibilities become more apparent. 

Imagine a tube with an amplification factor of 
about 250, and such a small grid-to-plate capacity 
that it has little tendency to oscillate even 
though the plate circuit be made highly inductive 
in reactance. The nearest approach is the stand- 
ard "high mu" tube with an amplification fac- 
tor of about 30, but, unfortunately, with 
sufficient capacity to make oscillation inevitable 
if sufficient inductance is included in its plate 
circuit to transfer energy efficiently to a subse- 
quent circuit. The screened grid tube, of which 
the ux-222 (cx-322) is the precursor, is a most 
unusual tube. What are its characteristics, its 
possibilities, its weak points? 

Physically it is complicated by having a fourth 
element within the glass bulb. Picture a cylin- 
drical construction with a 3.3-volt filament in 
the center, surrounded by a rather coarse grid, 
then, at some distance, another fine mesh grid, 
then a cylindrical plate, and the whole sur- 
rounded by another very fine grid of about forty 
spiral turns. The latter two grids, connected in 
parallel, form one electrode, thus constituting the 
extra element in the tube. It would be more 
accurate, for geometrical reasons, to call this 
tube a screened plate tube, but electrically, as 
we shall see, it is really the grid which is pro- 
tected from alternating voltages impressed upon 
the plate. 

The inner coarse grid is connected to a small 
metal cap which sits on top of the bulb, where the 
tip used to be, making the overall height about 
three quarters of an inch higher than standard 
tipless tubes. The screening grid connects to the 
usual grid terminal in the base so that the tube 
fits into the standard ux or uv socket. 

As pointed out in the December, 1927, RADIO 
BROADCAST by Mr. T. H. Nakken, there are two 
types of double-grid tubes, those in which the 
inner grid is positive, known as the space-charge 
tube, and those in which the outer or protective 
grid is positive. The ux-222 may be used either 

208 



way. Let us consider first its action as a shielded- 
grid device. In this case the outer grid is positive. 

We shall place 3.3 volts on the filament, make 
the inner grid negative, place about 45 volts on 
the shield, and read the plate current as the plate 
voltage is changed. The result is shown in Figs. I 
and 2. 

When this is done there are unusual results: 
First, the plate current rises, as is customary with 
increase in plate voltage. Then the plate current 
begins to decrease, giving the tube a characteris- 
tic like that of the electric arc, i.e., decreasing 
current with increased voltage; next, after a 
sharp minimum, the current rises almost per- 




FIG. 2 

If any reader of RADIO BROADCAST feels that he 
knows all there is to know about tubes, let him 
explain the sudden and extensive changes in 
plate current with change in plate voltage in- 
dicated in these graphs. With even greater screen 
voltages than are shown here, the plate current 
may be reduced to zero or even go negative (re- 
verse its direction of flow) at some positive plate 
voltage 



JANUARY, 1928 



THE SCREENED GRID TUBE 



209 



pendicularly and finally flattens out to become 
practically horizontal. All of this is contrary to 
what happens in standard tube practice and, to 
the student of physical phenomena, is extremely 
interesting. 

The slope of this plate voltage- plate current 
curve represents the plate impedance and, if 
plotted, an extraordinarily large scale graph would 
be required owing to the extent to which it 
changes. For example, in Fig. i it is 74,000 ohms 
near the origin, then it suddenly goes negative 
to the extent of 100,000 ohms, then positive 
about 10,000 ohms, and finally becomes about 
three-quarters of a megohm in value! The tube 
has a negative resistance, or a dynatron effect, 
at low plate voltages. 

These rapid and extensive changes in internal 
resistance are due to the varying proportions of 
current taken by the shield and the plate, both 
of which attract negative electrons, and to a 
certain amount of secondary emission which 
takes place within the tube. At the present mo- 
ment, however, the detailed explanation of these 
effects must give way to the more practical in- 
formation regarding the tube. We are more in- 
terested in this article in how the tube works than 
in "why." It is sufficient to state that the sum 
of the currents taken by the shield and the plate 
is constant, the plate current increasing when 
the shield takes fewer electrons, and vice versa. 
Uhder usual operating conditions, i.e., high 
plate voltages, the shield takes very little current 
indeed. 

Grid voltage -plate current curves appeared on 
page 1 1 1 of RADIO BROADCAST for December, 
1927, and will not be repeated here. They con- 
form to what one secures from other tubes of the 
general-purpose type. They indicate a mutual 
conductance of about 300 to 400 under average 
conditions, and an amplification factor of about 
250 to 300, values which should be compared to 
those of standard tubes in Table i. It is difficult 
to measure these factors on the ordinary bridge 
because of the extraordinarily high values of 
mu and plate impedance involved, and the better 
plan is to pick them from characteristic curves 
as we have done here. 

MATHEMATICS OF THE TUBE 

THE screened grid tube is designed primarily 
for radio-frequency amplification and, to 
understand its possibilities in amplifier circuits, 
we must examine somewhat more critically 
than usual the processes involved in the ordinary 
amplifier. Naturally we must have an input and 
output circuit, and for general analytical pur- 
poses we shall consider Fig. 3. 

The purpose of the transformer in such cir- 
cuits is not, as many would have us believe, to 
increase the voltage step-up from tube to tube, 
but to obtain a proper impedance for the ampli- 
fier plate circuit to look into. Mathematics will 
show that the maximum voltage amplification 
will be obtained when the effective primary 
impedance of the transformer is equal to the 
internal resistance of the tube, and that under 
these conditions this amplification is: 






K 



where R P = tube impedance, L = secondary 
inductance, R 5 = secondary resistance, and 
o> = 6.28 x frequency. 

If the effective resistance of the tuned circuit 
at resonance is higher than that of the preceding 
tube impedance, a step-down transformer must 
be used. This effective resistance may be found 
mathematically by substituting the proper values 
in the following expression : 




FIG. 3 

A diagrammatic representation of the ordinary 
interstage radio-frequency amplifier, consisting 
of a transformer, tuned to the frequency desired, 
connecting two tubes. The voltage gain at 
resonance is given in the form of two equations 

where L = inductance, Rs = high-frequency re- 
sistance, W = 6.28 x frequency. 

If we use an inductance of 250 microhenries 
having a resistance of 15 ohms at 1000 kc., this 
effective resistance will be: 

(250 x io-) ! x (6.28 x io) 
Ro = ' ' = 177,000 Ohms 

and if the previous tube is a 201 -A with an im- 
pedance of 12,000 ohms we shall be compelled 
to use a step-down transformer to secure maxi- 
mum amplification and to prevent short 
circuiting the secondary, to the impairment of 
the selectivity. Using a tube and coil of these 




FIG. 4 

For analytical purposes the two-winding trans- 
former of Fig. 3 may be replaced by this auto 
transformer. The same conditions for maximum 
voltage amplification obtain 

characteristics, and with the proper primary, 
the maximum amplication will be: 



K 



8 250 x 10-* x 6.28 x 10* 
max = i * y- 



15.0 (Approx.) 



12.000 x 15 

When any receiver designer states that he gets 
a uniform amplification per stage of much over 
this, he has neither used his mathematics nor 




Ro 



FIG. 5 

In the ordinary tube, some electrostatic lines of 
force connect the plate and grid because they 
are at different potential. This means, simply, 
that some capacity exists between them and it 
is this capacity that causes trouble in the usual 
high-frequency amplifier 



his vacuum-tube voltmeter to substantiate his 
statement. 

This transformer, with its two windings, can 
be replaced by an auto transformer for all prac- 
tical purposes, as shown in Fig. 4. An auto 
transformer, it will be remembered, is used in the 
" Universal" receiver previously described in this 
magazine and in the R. B. "Lab." Circuit, when 
the plate or primary coil is reversed. The imped- 
ance of the circuit, looked at from the preceding 
tube, must equal the impedance of that tube, 
and the position of the tap regulates the effective 
transformation ratio, so that this condition is 
realized, since the ratio of impedances across 
secondary and primary is equal to the square of 
the turns ratio. 

If we use a special radio-frequency tube with 
a higher amplication factor and higher impedance, 
such as the Ceco Type K, we must move the 
tap higher toward the grid end, or use more 
primary turns if we use a transformer, while if a 
1 12 type tube is used with its lower impedance, 
the tap can be brought further down. Table i 
gives essential data on existing tubes. The ap- 
proximate turns ratio, in the auto transformer 
case, can be found by substituting the value of 
plate impedance in the following equation: 

60000 

Turns Ratio = ^ . 

' Rp 

TABLE i 



TUBE 


V- 


R P 


G m 


TURNS 
RATIO 


199 


6.25 


16,600 


380 


I.QO 


2O I -A 


8.00 


12,000 


675 


2.25 


1 12 


8.00 


5,000 


1,000 


35 


2IO 


7.70 


5,000 


1-540 


3-5 


171 


3.00 


2,000 


1,500 


5-5 


222 


250.00 


7OO,OOO 


400 


i .0 


"K" 


13.00 


16,800 


780 


1-9 



Now all of this sounds simple to carry out but, 
practically, there are difficulties ahead most of 
them due to the fact that the tube does not act 
like a one-way street. Some traffic always goes in 
the opposite direction, because of the grid-plate 
capacity. As soon as we get the tap on our auto 
transformer moved high enough toward the grid 
end to secure maximum amplification, we include 
sufficient inductance in the plate circuit of the 
amplifier to make it oscillate, and trouble begins. 
Therefore we must do one of two things: we 
must either move the tap down, and lose ampli- 
fication because our equal impedance condition 
is no longer satisfied, or we must play neutraliza- 
tion tricks on the amplifier to keep it from oscil- 
lating, with perhaps slight loss in amplification 
as the price of stability. 

Here is where the screened grid comes in. 
Suppose, as in Fig. 5, we have the plate receiving 
electrons from the filament after passing through 
the grid in straight lines. Because of the fact that 
the grid and plate are at different potential there 
will be electrostatic lines between them, repre- 
sented by the curved lines. In other words, there 
is some connection between the plate and the 
grid, other than that produced by the passage of 
negative electrons. Now if we surround the plate 
by a fine grid which is grounded, as shown in Fig. 
6, these electrostatic lines do not reach the grid, 
and the latter is free to function only as a control 
on the flow of electrons. If, in addition, we make 
this shield positive with respect to the filament 
and grid, we neutralize some of the space charge 
which, in turn, boosts the amplification factor to 
a very high degree. 

If the plate is completely screened, the tube 
will be a one-way repeater, there will be no tend- 
ency to oscillate in the familiar tuned grid- 
tuned plate circuit, and a little mathematics will 



210 

show that the amplification is a factor of the 
mutual conductance of the tube and the external 
impedance. This external impedance is the effec- 
tive resistance of the tuned circuit, as already 
mentioned, and varies as shown below for average 
coils at usual frequencies. The possible voltage 
amplification may be easily calculated, with an 
assumed mutual conductance of 400 micromhos 
and an infinite plate impedance. 



RADIO BROADCAST 



FREQUENCY, 
KILOCYCLES 


Ro = LW OHMS 


AMPLIFICATION 
Gm x Ro 


Rs 


100 
1,000 

10,000 


400,000 
100,000 

10,000 


200 
40 
4 



These values of amplification are considerably 
greater than is possible with standard tubes such 
as we all use at the present time. At 1000 kc. 
(300 meters) the average gain in modern receivers 
may be as high as 10, and not many sets can do 
as well without some loss of stability. 

Actually, however, these values in the table 
with the 222 tube will not be attained, since the 
assumptions on which they were calculated, 
infinite plate impedance, no grid-plate capacity, 
and an effective resistance in the plate circuit of 
100,000 ohms, are not realized. Since the tube's 
internal impedance is of the order of a half 
megohm, or greater, which is considerably more 
than can be attained by average coils or by coils 
which will not cut side bands, there is no use in 




FIG. 6 

If a grounded shield is placed around the plate, 
the lines of force from grid to plate will be inter- 
rupted, and fewer changes of plate voltage will 
affect the grid in other words, the grid is 
shielded from the plate 



above. If this resistance is equal to that of the 
tube, approximately one-half the mu of the tube 
may be realized. With 100,000 ohms in the plate 
circuit approximately one seventh of the ampli- 
fication factor, or about 35 may be expected. 
For maximum voltage gain the effective resist- 



JANUARY, 1928 

amplifier, which had attached to its input a single 
wire antenna about 35 feet long, and a ground. 

With the brass box containing a Rice neutral- 
ized amplifier, using a aoi-A tube, and with the 
best position of the plate tap on the detector 
coil (see Fig. 8), the voltage upon the input to 
the detector was measured. Then the screened 
grid tube was used, the whole coil being used 
in its plate circuit, and the neutralization ap- 
paratus was done away with. The voltage was 
again measured with exactly the same input, and 
at the same frequency 500 kc. In this case the